diff --git a/src/gn/functions_target.cc b/src/gn/functions_target.cc
index 5ce0901..0864db5 100644
--- a/src/gn/functions_target.cc
+++ b/src/gn/functions_target.cc
@@ -740,8 +740,7 @@
 const char kSourceSet_Help[] =
     R"(source_set: Declare a source set target.
 
-  The language of a source_set target is determined by the extensions present
-  in its sources.
+  Only C-language source sets are supported at the moment.
 
 C-language source_sets
 
@@ -766,13 +765,6 @@
   not from the intermediate targets." There is no way to express this concept
   when linking multiple static libraries into a shared library.
 
-Rust-language source_sets
-
-  A Rust source set is a collection of sources that get passed along to the
-  final target that depends on it. No compilation is performed, and the source
-  files are simply added as dependencies on the eventual rustc invocation that
-  would produce a binary.
-
 Variables
 
 )" CONFIG_VALUES_VARS_HELP DEPS_VARS DEPENDENT_CONFIG_VARS GENERAL_TARGET_VARS;
diff --git a/src/gn/ninja_binary_target_writer.cc b/src/gn/ninja_binary_target_writer.cc
index 1a3e9b9..cde6be6 100644
--- a/src/gn/ninja_binary_target_writer.cc
+++ b/src/gn/ninja_binary_target_writer.cc
@@ -196,9 +196,49 @@
 void NinjaBinaryTargetWriter::AddSourceSetFiles(
     const Target* source_set,
     UniqueVector<OutputFile>* obj_files) const {
-  // Just add all sources to the list.
+  std::vector<OutputFile> tool_outputs;  // Prevent allocation in loop.
+
+  // Compute object files for all sources. Only link the first output from
+  // the tool if there are more than one.
   for (const auto& source : source_set->sources()) {
-    obj_files->push_back(OutputFile(settings_->build_settings(), source));
+    const char* tool_name = Tool::kToolNone;
+    if (source_set->GetOutputFilesForSource(source, &tool_name, &tool_outputs))
+      obj_files->push_back(tool_outputs[0]);
+  }
+
+  // Add MSVC precompiled header object files. GCC .gch files are not object
+  // files so they are omitted.
+  if (source_set->config_values().has_precompiled_headers()) {
+    if (source_set->source_types_used().Get(SourceFile::SOURCE_C)) {
+      const CTool* tool = source_set->toolchain()->GetToolAsC(CTool::kCToolCc);
+      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
+        GetPCHOutputFiles(source_set, CTool::kCToolCc, &tool_outputs);
+        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
+      }
+    }
+    if (source_set->source_types_used().Get(SourceFile::SOURCE_CPP)) {
+      const CTool* tool = source_set->toolchain()->GetToolAsC(CTool::kCToolCxx);
+      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
+        GetPCHOutputFiles(source_set, CTool::kCToolCxx, &tool_outputs);
+        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
+      }
+    }
+    if (source_set->source_types_used().Get(SourceFile::SOURCE_M)) {
+      const CTool* tool =
+          source_set->toolchain()->GetToolAsC(CTool::kCToolObjC);
+      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
+        GetPCHOutputFiles(source_set, CTool::kCToolObjC, &tool_outputs);
+        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
+      }
+    }
+    if (source_set->source_types_used().Get(SourceFile::SOURCE_MM)) {
+      const CTool* tool =
+          source_set->toolchain()->GetToolAsC(CTool::kCToolObjCxx);
+      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
+        GetPCHOutputFiles(source_set, CTool::kCToolObjCxx, &tool_outputs);
+        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
+      }
+    }
   }
 }
 
diff --git a/src/gn/ninja_binary_target_writer.h b/src/gn/ninja_binary_target_writer.h
index 7539ebb..69f5b50 100644
--- a/src/gn/ninja_binary_target_writer.h
+++ b/src/gn/ninja_binary_target_writer.h
@@ -65,8 +65,8 @@
   void WriteLibs(std::ostream& out, const Tool* tool);
   void WriteFrameworks(std::ostream& out, const Tool* tool);
 
-  virtual void AddSourceSetFiles(const Target* source_set,
-                                 UniqueVector<OutputFile>* obj_files) const;
+  void AddSourceSetFiles(const Target* source_set,
+                         UniqueVector<OutputFile>* obj_files) const;
 
   // Cached version of the prefix used for rule types for this toolchain.
   std::string rule_prefix_;
diff --git a/src/gn/ninja_c_binary_target_writer.cc b/src/gn/ninja_c_binary_target_writer.cc
index ebc2d17..5fa646f 100644
--- a/src/gn/ninja_c_binary_target_writer.cc
+++ b/src/gn/ninja_c_binary_target_writer.cc
@@ -639,54 +639,3 @@
   }
   return true;
 }
-
-// Appends the object files generated by the given source set to the given
-// output vector.
-void NinjaCBinaryTargetWriter::AddSourceSetFiles(
-    const Target* source_set,
-    UniqueVector<OutputFile>* obj_files) const {
-  std::vector<OutputFile> tool_outputs;  // Prevent allocation in loop.
-
-  // Compute object files for all sources. Only link the first output from
-  // the tool if there are more than one.
-  for (const auto& source : source_set->sources()) {
-    const char* tool_name = Tool::kToolNone;
-    if (source_set->GetOutputFilesForSource(source, &tool_name, &tool_outputs))
-      obj_files->push_back(tool_outputs[0]);
-  }
-
-  // Add MSVC precompiled header object files. GCC .gch files are not object
-  // files so they are omitted.
-  if (source_set->config_values().has_precompiled_headers()) {
-    if (source_set->source_types_used().Get(SourceFile::SOURCE_C)) {
-      const CTool* tool = source_set->toolchain()->GetToolAsC(CTool::kCToolCc);
-      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
-        GetPCHOutputFiles(source_set, CTool::kCToolCc, &tool_outputs);
-        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
-      }
-    }
-    if (source_set->source_types_used().Get(SourceFile::SOURCE_CPP)) {
-      const CTool* tool = source_set->toolchain()->GetToolAsC(CTool::kCToolCxx);
-      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
-        GetPCHOutputFiles(source_set, CTool::kCToolCxx, &tool_outputs);
-        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
-      }
-    }
-    if (source_set->source_types_used().Get(SourceFile::SOURCE_M)) {
-      const CTool* tool =
-          source_set->toolchain()->GetToolAsC(CTool::kCToolObjC);
-      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
-        GetPCHOutputFiles(source_set, CTool::kCToolObjC, &tool_outputs);
-        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
-      }
-    }
-    if (source_set->source_types_used().Get(SourceFile::SOURCE_MM)) {
-      const CTool* tool =
-          source_set->toolchain()->GetToolAsC(CTool::kCToolObjCxx);
-      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
-        GetPCHOutputFiles(source_set, CTool::kCToolObjCxx, &tool_outputs);
-        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
-      }
-    }
-  }
-}
diff --git a/src/gn/ninja_c_binary_target_writer.h b/src/gn/ninja_c_binary_target_writer.h
index 55cc0fc..ee6b6ac 100644
--- a/src/gn/ninja_c_binary_target_writer.h
+++ b/src/gn/ninja_c_binary_target_writer.h
@@ -22,11 +22,6 @@
 
   void Run() override;
 
- protected:
-  // Adds source_set files to the list of object files.
-  void AddSourceSetFiles(const Target* source_set,
-                         UniqueVector<OutputFile>* obj_files) const override;
-
  private:
   using OutputFileSet = std::set<OutputFile>;
 
diff --git a/src/gn/ninja_rust_binary_target_writer.cc b/src/gn/ninja_rust_binary_target_writer.cc
index 8a907bb..abe903f 100644
--- a/src/gn/ninja_rust_binary_target_writer.cc
+++ b/src/gn/ninja_rust_binary_target_writer.cc
@@ -122,72 +122,68 @@
   // -Ldependency rustdeps, and non-public source_sets get passed in as normal
   // source files
   UniqueVector<OutputFile> deps;
-  AddSourceSetFiles(target_, &deps);
-  if (target_->output_type() == Target::SOURCE_SET) {
-    WriteSharedVars(target_->toolchain()->substitution_bits());
-    WriteSourceSetStamp(deps.vector());
-  } else {
-    WriteCompilerVars();
-    UniqueVector<const Target*> linkable_deps;
-    UniqueVector<const Target*> non_linkable_deps;
-    UniqueVector<const Target*> framework_deps;
-    GetDeps(&deps, &linkable_deps, &non_linkable_deps, &framework_deps);
+  DCHECK(target_->output_type() != Target::SOURCE_SET);
+  WriteCompilerVars();
+  UniqueVector<const Target*> linkable_deps;
+  UniqueVector<const Target*> non_linkable_deps;
+  UniqueVector<const Target*> framework_deps;
+  GetDeps(&deps, &linkable_deps, &non_linkable_deps, &framework_deps);
+  AppendSourcesToImplicitDeps(&deps);
 
-    if (!input_dep.value().empty())
-      order_only_deps.push_back(input_dep);
+  if (!input_dep.value().empty())
+    order_only_deps.push_back(input_dep);
 
-    std::vector<OutputFile> rustdeps;
-    std::vector<OutputFile> nonrustdeps;
-    for (const auto* framework_dep : framework_deps) {
-      order_only_deps.push_back(framework_dep->dependency_output_file());
-    }
-    for (const auto* non_linkable_dep : non_linkable_deps) {
-      if (non_linkable_dep->source_types_used().RustSourceUsed() &&
-          non_linkable_dep->output_type() != Target::SOURCE_SET) {
-        rustdeps.push_back(non_linkable_dep->dependency_output_file());
-      }
-      order_only_deps.push_back(non_linkable_dep->dependency_output_file());
-    }
-    for (const auto* linkable_dep : linkable_deps) {
-      if (linkable_dep->source_types_used().RustSourceUsed()) {
-        rustdeps.push_back(linkable_dep->link_output_file());
-      } else {
-        nonrustdeps.push_back(linkable_dep->link_output_file());
-      }
-      deps.push_back(linkable_dep->dependency_output_file());
-    }
-
-    // Rust libraries specified by paths.
-    for (ConfigValuesIterator iter(target_); !iter.done(); iter.Next()) {
-      const ConfigValues& cur = iter.cur();
-      for (const auto& e : cur.externs()) {
-        if (e.second.is_source_file()) {
-          deps.push_back(
-              OutputFile(settings_->build_settings(), e.second.source_file()));
-        }
-      }
-    }
-
-    std::vector<OutputFile> transitive_rustlibs;
-    for (const auto* dep :
-         target_->rust_values().transitive_libs().GetOrdered()) {
-      if (dep->source_types_used().RustSourceUsed()) {
-        transitive_rustlibs.push_back(dep->dependency_output_file());
-      }
-    }
-
-    std::vector<OutputFile> tool_outputs;
-    SubstitutionWriter::ApplyListToLinkerAsOutputFile(
-        target_, tool_, tool_->outputs(), &tool_outputs);
-    WriteCompilerBuildLine(target_->rust_values().crate_root(), deps.vector(),
-                           order_only_deps, tool_->name(), tool_outputs);
-
-    std::vector<const Target*> extern_deps(linkable_deps.vector());
-    std::copy(non_linkable_deps.begin(), non_linkable_deps.end(),
-              std::back_inserter(extern_deps));
-    WriteExterns(extern_deps);
-    WriteRustdeps(transitive_rustlibs, rustdeps, nonrustdeps);
+  std::vector<OutputFile> rustdeps;
+  std::vector<OutputFile> nonrustdeps;
+  for (const auto* framework_dep : framework_deps) {
+    order_only_deps.push_back(framework_dep->dependency_output_file());
   }
+  for (const auto* non_linkable_dep : non_linkable_deps) {
+    if (non_linkable_dep->source_types_used().RustSourceUsed() &&
+        non_linkable_dep->output_type() != Target::SOURCE_SET) {
+      rustdeps.push_back(non_linkable_dep->dependency_output_file());
+    }
+    order_only_deps.push_back(non_linkable_dep->dependency_output_file());
+  }
+  for (const auto* linkable_dep : linkable_deps) {
+    if (linkable_dep->source_types_used().RustSourceUsed()) {
+      rustdeps.push_back(linkable_dep->link_output_file());
+    } else {
+      nonrustdeps.push_back(linkable_dep->link_output_file());
+    }
+    deps.push_back(linkable_dep->dependency_output_file());
+  }
+
+  // Rust libraries specified by paths.
+  for (ConfigValuesIterator iter(target_); !iter.done(); iter.Next()) {
+    const ConfigValues& cur = iter.cur();
+    for (const auto& e : cur.externs()) {
+      if (e.second.is_source_file()) {
+        deps.push_back(
+            OutputFile(settings_->build_settings(), e.second.source_file()));
+      }
+    }
+  }
+
+  std::vector<OutputFile> transitive_rustlibs;
+  for (const auto* dep :
+       target_->rust_values().transitive_libs().GetOrdered()) {
+    if (dep->source_types_used().RustSourceUsed()) {
+      transitive_rustlibs.push_back(dep->dependency_output_file());
+    }
+  }
+
+  std::vector<OutputFile> tool_outputs;
+  SubstitutionWriter::ApplyListToLinkerAsOutputFile(
+      target_, tool_, tool_->outputs(), &tool_outputs);
+  WriteCompilerBuildLine(target_->rust_values().crate_root(), deps.vector(),
+                         order_only_deps, tool_->name(), tool_outputs);
+
+  std::vector<const Target*> extern_deps(linkable_deps.vector());
+  std::copy(non_linkable_deps.begin(), non_linkable_deps.end(),
+            std::back_inserter(extern_deps));
+  WriteExterns(extern_deps);
+  WriteRustdeps(transitive_rustlibs, rustdeps, nonrustdeps);
 }
 
 void NinjaRustBinaryTargetWriter::WriteCompilerVars() {
@@ -205,6 +201,18 @@
   WriteSharedVars(subst);
 }
 
+void NinjaRustBinaryTargetWriter::AppendSourcesToImplicitDeps(
+    UniqueVector<OutputFile>* deps) const {
+  // Only the crate_root file needs to be given to rustc as input.
+  // Any other 'sources' are just implicit deps.
+  // Most Rust targets won't bother specifying the "sources =" line
+  // because it is handled sufficiently by crate_root and the generation
+  // of depfiles by rustc. But for those which do...
+  for (const auto& source : target_->sources()) {
+    deps->push_back(OutputFile(settings_->build_settings(), source));
+  }
+}
+
 void NinjaRustBinaryTargetWriter::WriteExterns(
     const std::vector<const Target*>& deps) {
   out_ << "  externs =";
diff --git a/src/gn/ninja_rust_binary_target_writer.h b/src/gn/ninja_rust_binary_target_writer.h
index cd845d5..4d6e146 100644
--- a/src/gn/ninja_rust_binary_target_writer.h
+++ b/src/gn/ninja_rust_binary_target_writer.h
@@ -26,9 +26,10 @@
                     const std::vector<OutputFile>& order_only_deps);
   void WriteExterns(const std::vector<const Target*>& deps);
   void WriteRustdeps(const std::vector<OutputFile>& transitive_rustdeps,
-      const std::vector<OutputFile>& rustdeps,
-      const std::vector<OutputFile>& nonrustdeps);
+                     const std::vector<OutputFile>& rustdeps,
+                     const std::vector<OutputFile>& nonrustdeps);
   void WriteEdition();
+  void AppendSourcesToImplicitDeps(UniqueVector<OutputFile>* deps) const;
 
   const RustTool* tool_;
 
diff --git a/src/gn/ninja_rust_binary_target_writer_unittest.cc b/src/gn/ninja_rust_binary_target_writer_unittest.cc
index ded290a..70a7d00 100644
--- a/src/gn/ninja_rust_binary_target_writer_unittest.cc
+++ b/src/gn/ninja_rust_binary_target_writer_unittest.cc
@@ -26,39 +26,13 @@
   target.sources().push_back(SourceFile("//foo/main.rs"));
   target.source_types_used().Set(SourceFile::SOURCE_RS);
   target.SetToolchain(setup.toolchain());
-  ASSERT_TRUE(target.OnResolved(&err));
-
-  // Source set itself.
-  {
-    std::ostringstream out;
-    NinjaRustBinaryTargetWriter writer(&target, out);
-    writer.Run();
-
-    const char expected[] =
-        "root_out_dir = .\n"
-        "target_out_dir = obj/foo\n"
-        "target_output_name = bar\n"
-        "\n"
-        "build obj/foo/bar.stamp: stamp ../../foo/input1.rs "
-        "../../foo/main.rs\n";
-    std::string out_str = out.str();
-    EXPECT_EQ(expected, out_str) << out_str;
-  }
+  ASSERT_FALSE(target.OnResolved(&err));
 }
 
 TEST_F(NinjaRustBinaryTargetWriterTest, RustExecutable) {
   Err err;
   TestWithScope setup;
 
-  Target source_set(setup.settings(), Label(SourceDir("//foo/"), "sources"));
-  source_set.set_output_type(Target::SOURCE_SET);
-  source_set.visibility().SetPublic();
-  source_set.sources().push_back(SourceFile("//foo/input1.rs"));
-  source_set.sources().push_back(SourceFile("//foo/input2.rs"));
-  source_set.source_types_used().Set(SourceFile::SOURCE_RS);
-  source_set.SetToolchain(setup.toolchain());
-  ASSERT_TRUE(source_set.OnResolved(&err));
-
   Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
   target.set_output_type(Target::EXECUTABLE);
   target.visibility().SetPublic();
@@ -68,7 +42,6 @@
   target.source_types_used().Set(SourceFile::SOURCE_RS);
   target.rust_values().set_crate_root(main);
   target.rust_values().crate_name() = "foo_bar";
-  target.private_deps().push_back(LabelTargetPair(&source_set));
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
 
@@ -89,8 +62,7 @@
         "target_output_name = bar\n"
         "\n"
         "build ./foo_bar: rust_bin ../../foo/main.rs | ../../foo/input3.rs "
-        "../../foo/main.rs ../../foo/input1.rs ../../foo/input2.rs || "
-        "obj/foo/sources.stamp\n"
+        "../../foo/main.rs\n"
         "  externs =\n"
         "  rustdeps =\n";
     std::string out_str = out.str();
@@ -495,15 +467,6 @@
   Err err;
   TestWithScope setup;
 
-  Target source_set(setup.settings(), Label(SourceDir("//foo/"), "sources"));
-  source_set.set_output_type(Target::SOURCE_SET);
-  source_set.visibility().SetPublic();
-  source_set.sources().push_back(SourceFile("//foo/input1.rs"));
-  source_set.sources().push_back(SourceFile("//foo/input2.rs"));
-  source_set.source_types_used().Set(SourceFile::SOURCE_RS);
-  source_set.SetToolchain(setup.toolchain());
-  ASSERT_TRUE(source_set.OnResolved(&err));
-
   Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
   target.set_output_type(Target::EXECUTABLE);
   target.visibility().SetPublic();
@@ -515,7 +478,6 @@
   target.set_output_dir(SourceDir("//out/Debug/foo/"));
   target.rust_values().set_crate_root(main);
   target.rust_values().crate_name() = "foo_bar";
-  target.private_deps().push_back(LabelTargetPair(&source_set));
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
 
@@ -536,8 +498,7 @@
         "target_output_name = bar\n"
         "\n"
         "build ./foo_bar.exe: rust_bin ../../foo/main.rs | ../../foo/input3.rs "
-        "../../foo/main.rs ../../foo/input1.rs ../../foo/input2.rs || "
-        "obj/foo/sources.stamp\n"
+        "../../foo/main.rs\n"
         "  externs =\n"
         "  rustdeps =\n";
     std::string out_str = out.str();
diff --git a/src/gn/target.cc b/src/gn/target.cc
index 93ad7c0..ef91167 100644
--- a/src/gn/target.cc
+++ b/src/gn/target.cc
@@ -383,6 +383,8 @@
   if (!FillOutputFiles(err))
     return false;
 
+  if (!CheckSourceSetLanguages(err))
+    return false;
   if (!CheckVisibility(err))
     return false;
   if (!CheckTestonly(err))
@@ -934,6 +936,17 @@
   return true;
 }
 
+bool Target::CheckSourceSetLanguages(Err* err) const {
+  if (output_type() == Target::SOURCE_SET &&
+      source_types_used().RustSourceUsed()) {
+    *err = Err(defined_from(), "source_set contained Rust code.",
+               label().GetUserVisibleName(false) +
+                   " has Rust code. Only C/C++ source_sets are supported.");
+    return false;
+  }
+  return true;
+}
+
 bool Target::CheckTestonly(Err* err) const {
   // If the current target is marked testonly, it can include both testonly
   // and non-testonly targets, so there's nothing to check.
diff --git a/src/gn/target.h b/src/gn/target.h
index 700859c..44f7e17 100644
--- a/src/gn/target.h
+++ b/src/gn/target.h
@@ -407,6 +407,7 @@
   bool CheckAssertNoDeps(Err* err) const;
   void CheckSourcesGenerated() const;
   void CheckSourceGenerated(const SourceFile& source) const;
+  bool CheckSourceSetLanguages(Err* err) const;
 
   OutputType output_type_ = UNKNOWN;
   std::string output_name_;