diff --git a/src/gn/function_toolchain_unittest.cc b/src/gn/function_toolchain_unittest.cc
index ba4bfb6..74cbef9 100644
--- a/src/gn/function_toolchain_unittest.cc
+++ b/src/gn/function_toolchain_unittest.cc
@@ -43,6 +43,7 @@
     TestParseInput input(
         R"(toolchain("good") {
           tool("link") {
+            command = "link"
             outputs = [ "foo" ]
             runtime_outputs = [ "foo" ]
           }
@@ -116,12 +117,27 @@
   }
 }
 
+TEST_F(FunctionToolchain, Command) {
+  TestWithScope setup;
+
+  TestParseInput input(
+      R"(toolchain("missing_command") {
+        tool("cxx") {}
+      })");
+  ASSERT_FALSE(input.has_error());
+
+  Err err;
+  input.parsed()->Execute(setup.scope(), &err);
+  ASSERT_TRUE(err.has_error()) << err.message();
+}
+
 TEST_F(FunctionToolchain, CommandLauncher) {
   TestWithScope setup;
 
   TestParseInput input(
       R"(toolchain("good") {
         tool("cxx") {
+          command = "cxx"
           command_launcher = "/usr/goma/gomacc"
         }
       })");
diff --git a/src/gn/ninja_toolchain_writer.cc b/src/gn/ninja_toolchain_writer.cc
index e38187f..3793ab0 100644
--- a/src/gn/ninja_toolchain_writer.cc
+++ b/src/gn/ninja_toolchain_writer.cc
@@ -132,8 +132,6 @@
     const SubstitutionPattern& command,
     const EscapeOptions& options) {
   CHECK(!command.empty()) << "Command should not be empty";
-  if (command.empty())
-    return;
   out_ << kIndent << name << " = " ;
   if (!launcher.empty())
     out_ << launcher << " ";
diff --git a/src/gn/tool.cc b/src/gn/tool.cc
index 3b29775..99b7525 100644
--- a/src/gn/tool.cc
+++ b/src/gn/tool.cc
@@ -205,6 +205,14 @@
       !ReadLabel(scope, "pool", toolchain->label(), &pool_, err)) {
     return false;
   }
+  const bool command_is_required = name_ != GeneralTool::kGeneralToolAction;
+  if (command_.empty() == command_is_required) {
+    *err = Err(defined_from(), "This tool's command is bad.",
+               command_is_required
+                   ? "This tool requires \"command\" to be defined."
+                   : "This tool doesn't support \"command\".");
+    return false;
+  }
   return true;
 }