4 files changed, 39 insertions, 2 deletions
diff --git a/objectivec/GPBMessage_PackagePrivate.h b/objectivec/GPBMessage_PackagePrivate.h
index 820bb7b4..366e5bbf 100644
--- a/objectivec/GPBMessage_PackagePrivate.h
+++ b/objectivec/GPBMessage_PackagePrivate.h
@@ -34,8 +34,6 @@
 
 #import "GPBMessage.h"
 
-#import <stdatomic.h>
-
 // TODO: Remove this import. Older generated code use the OSAtomic* apis,
 // so anyone that hasn't regenerated says building by having this. After
 // enough time has passed, this likely can be removed as folks should have
diff --git a/objectivec/google/protobuf/Struct.pbobjc.m b/objectivec/google/protobuf/Struct.pbobjc.m
index dff2f844..6d9d7b75 100644
--- a/objectivec/google/protobuf/Struct.pbobjc.m
+++ b/objectivec/google/protobuf/Struct.pbobjc.m
@@ -13,6 +13,8 @@
  #import "GPBProtocolBuffers_RuntimeSupport.h"
 #endif
 
+#import <stdatomic.h>
+
 #if GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS
  #import <Protobuf/Struct.pbobjc.h>
 #else
diff --git a/objectivec/google/protobuf/Type.pbobjc.m b/objectivec/google/protobuf/Type.pbobjc.m
index 06795308..981ae4d4 100644
--- a/objectivec/google/protobuf/Type.pbobjc.m
+++ b/objectivec/google/protobuf/Type.pbobjc.m
@@ -13,6 +13,8 @@
  #import "GPBProtocolBuffers_RuntimeSupport.h"
 #endif
 
+#import <stdatomic.h>
+
 #if GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS
  #import <Protobuf/Type.pbobjc.h>
  #import <Protobuf/Any.pbobjc.h>
diff --git a/src/google/protobuf/compiler/objectivec/objectivec_file.cc b/src/google/protobuf/compiler/objectivec/objectivec_file.cc
index 954b2688..a249c71b 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_file.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_file.cc
@@ -56,6 +56,20 @@ const int32 GOOGLE_PROTOBUF_OBJC_VERSION = 30002;
 
 const char* kHeaderExtension = ".pbobjc.h";
 
+// Checks if a message contains any enums definitions (on the message or
+// a nested message under it).
+bool MessageContainsEnums(const Descriptor* message) {
+  if (message->enum_type_count() > 0) {
+    return true;
+  }
+  for (int i = 0; i < message->nested_type_count(); i++) {
+    if (MessageContainsEnums(message->nested_type(i))) {
+      return true;
+    }
+  }
+  return false;
+}
+
 // Checks if a message contains any extension definitions (on the message or
 // a nested message under it).
 bool MessageContainsExtensions(const Descriptor* message) {
@@ -70,6 +84,20 @@ bool MessageContainsExtensions(const Descriptor* message) {
   return false;
 }
 
+// Checks if the file contains any enum definitions (at the root or
+// nested under a message).
+bool FileContainsEnums(const FileDescriptor* file) {
+  if (file->enum_type_count() > 0) {
+    return true;
+  }
+  for (int i = 0; i < file->message_type_count(); i++) {
+    if (MessageContainsEnums(file->message_type(i))) {
+      return true;
+    }
+  }
+  return false;
+}
+
 // Checks if the file contains any extensions definitions (at the root or
 // nested under a message).
 bool FileContainsExtensions(const FileDescriptor* file) {
@@ -311,6 +339,13 @@ void FileGenerator::GenerateSource(io::Printer *printer) {
   // #import the runtime support.
   PrintFileRuntimePreamble(printer, "GPBProtocolBuffers_RuntimeSupport.h");
 
+  // Enums use atomic in the generated code, so add the system import as needed.
+  if (FileContainsEnums(file_)) {
+    printer->Print(
+        "#import <stdatomic.h>\n"
+        "\n");
+  }
+
   vector<const FileDescriptor*> deps_with_extensions;
   CollectMinimalFileDepsContainingExtensions(file_, &deps_with_extensions);