diff --git a/src/share/classes/java/lang/invoke/LambdaForm.java b/src/share/classes/java/lang/invoke/LambdaForm.java
index a5e40ed52114d6c73fe5b1e5214c23061526668c..a8291e273c0fcb23aa1653219d28a46680320dd6 100644
--- a/src/share/classes/java/lang/invoke/LambdaForm.java
+++ b/src/share/classes/java/lang/invoke/LambdaForm.java
@@ -482,7 +482,7 @@ class LambdaForm {
                 assert(m.getName().equals("interpret" + sig.substring(sig.indexOf('_'))));
                 LambdaForm form = new LambdaForm(sig);
                 form.vmentry = m;
-                mt.form().setCachedLambdaForm(MethodTypeForm.LF_COUNTER, form);
+                form = mt.form().setCachedLambdaForm(MethodTypeForm.LF_COUNTER, form);
                 // FIXME: get rid of PREPARED_FORMS; use MethodTypeForm cache only
                 forms.put(sig, form);
             }
diff --git a/src/share/classes/java/lang/invoke/MethodHandleImpl.java b/src/share/classes/java/lang/invoke/MethodHandleImpl.java
index cdf6e5a75ce7d71d5712d62060c9dc66f390e5d1..ee1584f80f64307c12bb6ea07c836e66ab46fc2a 100644
--- a/src/share/classes/java/lang/invoke/MethodHandleImpl.java
+++ b/src/share/classes/java/lang/invoke/MethodHandleImpl.java
@@ -692,8 +692,7 @@ import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;
 
         lform = new LambdaForm("guardWithCatch", lambdaType.parameterCount(), names);
 
-        basicType.form().setCachedLambdaForm(MethodTypeForm.LF_GWC, lform);
-        return lform;
+        return basicType.form().setCachedLambdaForm(MethodTypeForm.LF_GWC, lform);
     }
 
     static
diff --git a/src/share/classes/java/lang/invoke/MethodTypeForm.java b/src/share/classes/java/lang/invoke/MethodTypeForm.java
index ee5e6221b11dfd34ef8d002dbba6becbd7499598..d34a2998caba9cd8cc319e60ffe8501e9bcf98c5 100644
--- a/src/share/classes/java/lang/invoke/MethodTypeForm.java
+++ b/src/share/classes/java/lang/invoke/MethodTypeForm.java
@@ -91,8 +91,10 @@ final class MethodTypeForm {
         return lambdaForms[which];
     }
 
-    public LambdaForm setCachedLambdaForm(int which, LambdaForm form) {
-        // Should we perform some sort of CAS, to avoid racy duplication?
+    synchronized public LambdaForm setCachedLambdaForm(int which, LambdaForm form) {
+        // Simulate a CAS, to avoid racy duplication of results.
+        LambdaForm prev = lambdaForms[which];
+        if (prev != null) return prev;
         return lambdaForms[which] = form;
     }