diff --git a/Source/Additions/NSError+GNUstepBase.m b/Source/Additions/NSError+GNUstepBase.m
index 98e3f6db4..818c126d4 100644
--- a/Source/Additions/NSError+GNUstepBase.m
+++ b/Source/Additions/NSError+GNUstepBase.m
@@ -28,6 +28,7 @@
 
 #import "Foundation/NSDictionary.h"
 #import "Foundation/NSError.h"
+#import "Foundation/NSLock.h"
 #import "GSPrivate.h"
 
 /**