diff --git a/React/Base/RCTUtils.h b/React/Base/RCTUtils.h
index 811c66d1a..30febd5a3 100644
--- a/React/Base/RCTUtils.h
+++ b/React/Base/RCTUtils.h
@@ -97,7 +97,7 @@ RCT_EXTERN double RCTZeroIfNaN(double value);
 RCT_EXTERN NSURL *RCTDataURL(NSString *mimeType, NSData *data);
 
 // Gzip functionality - compression level in range 0 - 1 (-1 for default)
-RCT_EXTERN NSData *RCTGzipData(NSData *__nullable data, float level);
+RCT_EXTERN NSData *__nullable RCTGzipData(NSData *__nullable data, float level);
 
 // Returns the relative path within the main bundle for an absolute URL
 // (or nil, if the URL does not specify a path within the main bundle)
diff --git a/React/Base/RCTUtils.m b/React/Base/RCTUtils.m
index d2a0916b3..7b69da74b 100644
--- a/React/Base/RCTUtils.m
+++ b/React/Base/RCTUtils.m
@@ -451,7 +451,7 @@ BOOL RCTIsGzippedData(NSData *__nullable data)
   return (data.length >= 2 && bytes[0] == 0x1f && bytes[1] == 0x8b);
 }
 
-NSData *RCTGzipData(NSData *__nullable input, float level)
+NSData *__nullable RCTGzipData(NSData *__nullable input, float level)
 {
   if (input.length == 0 || RCTIsGzippedData(input)) {
     return input;