diff -r 0ba758a2b6f0 src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/meta/HotSpotForeignCallsProviderImpl.java
--- a/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/meta/HotSpotForeignCallsProviderImpl.java	Thu Mar 05 03:27:17 2020 -0500
+++ b/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/meta/HotSpotForeignCallsProviderImpl.java	Thu Mar 05 11:52:43 2020 +0100
@@ -152,6 +152,10 @@
                     LocationIdentity... killedLocations) {
         Class<?> resultType = descriptor.getResultType();
         assert address != 0 : descriptor;
+        if (transition == SAFEPOINT && !resultType.isPrimitive() && !Word.class.isAssignableFrom(resultType)) {
+            System.out.printf("resultType == Word.class is %s%n", resultType == Word.class);
+            System.out.printf("Word.class.isAssignableFrom(resultType) is %s%n", Word.class.isAssignableFrom(resultType));
+        }
         assert transition != SAFEPOINT || resultType.isPrimitive() || Word.class.isAssignableFrom(resultType) : "non-leaf foreign calls must return objects in thread local storage: " + descriptor;
         return register(HotSpotForeignCallLinkageImpl.create(metaAccess,
                         codeCache,