diff --git a/tools/gn/function_set_defaults.cc b/tools/gn/function_set_defaults.cc
index 4efb929..7f26b44 100644
--- a/tools/gn/function_set_defaults.cc
+++ b/tools/gn/function_set_defaults.cc
@@ -27,9 +27,14 @@
     "\n"
     "  set_defaults can be used for built-in target types (\"executable\",\n"
     "  \"shared_library\", etc.) and custom ones defined via the \"template\"\n"
-    "  command.\n"
+    "  command. It can be called more than once and the most recent call in\n"
+    "  any scope will apply, but there is no way to refer to the previous\n"
+    "  defaults and modify them (each call to set_defaults must supply a\n"
+    "  complete list of all defaults it wants). If you want to share\n"
+    "  defaults, store them in a separate variable.\n"
     "\n"
-    "Example:\n"
+    "Example\n"
+    "\n"
     "  set_defaults(\"static_library\") {\n"
     "    configs = [ \"//tools/mything:settings\" ]\n"
     "  }\n"
@@ -49,27 +54,6 @@
     return Value();
   const std::string& target_type(args[0].string_value());
 
-  // Ensure there aren't defaults already set.
-  //
-  // It might be nice to allow multiple calls set mutate the defaults. The
-  // main case for this is where some local portions of the code want
-  // additional defaults they specify in an imported file.
-  //
-  // Currently, we don't allow imports to clobber anything, so this wouldn't
-  // work. Additionally, allowing this would be undesirable since we don't
-  // want multiple imports to each try to set defaults, since it might look
-  // like the defaults are modified by each one in sequence, while in fact
-  // imports would always clobber previous values and it would be confusing.
-  //
-  // If we wanted this, the solution would be to allow imports to overwrite
-  // target defaults set up by the default build config only. That way there
-  // are no ordering issues, but this would be more work.
-  if (scope->GetTargetDefaults(target_type)) {
-    *err = Err(function->function(),
-               "This target type defaults were already set.");
-    return Value();
-  }
-
   if (!block) {
     FillNeedsBlockError(function, err);
     return Value();
diff --git a/tools/gn/scope.cc b/tools/gn/scope.cc
index 3869f3b..8e9230d 100644
--- a/tools/gn/scope.cc
+++ b/tools/gn/scope.cc
@@ -298,18 +298,27 @@
     }
 
     if (!options.clobber_existing) {
-      if (dest->GetTargetDefaults(current_name)) {
-        // TODO(brettw) it would be nice to know the origin of a
-        // set_target_defaults so we can give locations for the colliding target
-        // defaults.
-        std::string desc_string(desc_for_err);
-        *err = Err(node_for_err, "Target defaults collision.",
-            "This " + desc_string + " contains target defaults for\n"
-            "\"" + current_name + "\" which would clobber one for the\n"
-            "same target type in your current scope. It's unfortunate that I'm "
-            "too stupid\nto tell you the location of where the target defaults "
-            "were set. Usually\nthis happens in the BUILDCONFIG.gn file.");
-        return false;
+      const Scope* dest_defaults = dest->GetTargetDefaults(current_name);
+      if (dest_defaults) {
+        if (RecordMapValuesEqual(pair.second->values_,
+                                 dest_defaults->values_)) {
+          // Values of the two defaults are equivalent, just ignore the
+          // collision.
+          continue;
+        } else {
+          // TODO(brettw) it would be nice to know the origin of a
+          // set_target_defaults so we can give locations for the colliding
+          // target defaults.
+          std::string desc_string(desc_for_err);
+          *err = Err(node_for_err, "Target defaults collision.",
+              "This " + desc_string + " contains target defaults for\n"
+              "\"" + current_name + "\" which would clobber one for the\n"
+              "same target type in your current scope. It's unfortunate that "
+              "I'm too stupid\nto tell you the location of where the target "
+              "defaults were set. Usually\nthis happens in the BUILDCONFIG.gn "
+              "file or in a related .gni file.\n");
+          return false;
+        }
       }
     }
 
@@ -404,14 +413,7 @@
 }
 
 Scope* Scope::MakeTargetDefaults(const std::string& target_type) {
-  if (GetTargetDefaults(target_type))
-    return nullptr;
-
   std::unique_ptr<Scope>& dest = target_defaults_[target_type];
-  if (dest) {
-    NOTREACHED();  // Already set.
-    return dest.get();
-  }
   dest = base::WrapUnique(new Scope(settings_));
   return dest.get();
 }
@@ -514,3 +516,17 @@
   DCHECK(programmatic_providers_.find(p) != programmatic_providers_.end());
   programmatic_providers_.erase(p);
 }
+
+// static
+bool Scope::RecordMapValuesEqual(const RecordMap& a, const RecordMap& b) {
+  if (a.size() != b.size())
+    return false;
+  for (const auto& pair : a) {
+    const auto& found_b = b.find(pair.first);
+    if (found_b == b.end())
+      return false;  // Item in 'a' but not 'b'.
+    if (pair.second.value != found_b->second.value)
+      return false;  // Values for variable in 'a' and 'b' are different.
+  }
+  return true;
+}
diff --git a/tools/gn/scope.h b/tools/gn/scope.h
index e9bd139..685f840 100644
--- a/tools/gn/scope.h
+++ b/tools/gn/scope.h
@@ -229,8 +229,7 @@
   // change, we don't have to copy its values).
   std::unique_ptr<Scope> MakeClosure() const;
 
-  // Makes an empty scope with the given name. Returns NULL if the name is
-  // already set.
+  // Makes an empty scope with the given name. Overwrites any existing one.
   Scope* MakeTargetDefaults(const std::string& target_type);
 
   // Gets the scope associated with the given target name, or null if it hasn't
@@ -311,9 +310,16 @@
     Value value;
   };
 
+  typedef base::hash_map<base::StringPiece, Record, base::StringPieceHash>
+      RecordMap;
+
   void AddProvider(ProgrammaticProvider* p);
   void RemoveProvider(ProgrammaticProvider* p);
 
+  // Returns true if the two RecordMaps contain the same values (the origins
+  // of the values may be different).
+  static bool RecordMapValuesEqual(const RecordMap& a, const RecordMap& b);
+
   // Scopes can have no containing scope (both null), a mutable containing
   // scope, or a const containing scope. The reason is that when we're doing
   // a new target, we want to refer to the base_config scope which will be read
@@ -329,8 +335,6 @@
   // for more.
   unsigned mode_flags_;
 
-  typedef base::hash_map<base::StringPiece, Record, base::StringPieceHash>
-      RecordMap;
   RecordMap values_;
 
   // Note that this can't use string pieces since the names are constructed from