diff --git a/library/src/main/java/com/bumptech/glide/load/resource/transcode/TranscoderRegistry.java b/library/src/main/java/com/bumptech/glide/load/resource/transcode/TranscoderRegistry.java
index 840bf7d9da38c33e27f8e3cb8bcd3866ad21ca31..adc854c7f61963e4873a15898a3f29f4b72a5689 100644
--- a/library/src/main/java/com/bumptech/glide/load/resource/transcode/TranscoderRegistry.java
+++ b/library/src/main/java/com/bumptech/glide/load/resource/transcode/TranscoderRegistry.java
@@ -44,8 +44,11 @@ public class TranscoderRegistry {
             // we know they're the same type (Z and R)
             return (ResourceTranscoder<Z, R>) UnitTranscoder.get();
         }
-        GET_KEY.set(decodedClass, transcodedClass);
-        ResourceTranscoder<?, ?> result = factories.get(GET_KEY);
+        final ResourceTranscoder<?, ?> result;
+        synchronized (GET_KEY) {
+            GET_KEY.set(decodedClass, transcodedClass);
+            result = factories.get(GET_KEY);
+        }
         if (result == null) {
             throw new IllegalArgumentException("No transcoder registered for " + decodedClass + " and "
                     + transcodedClass);