Index: /trunk/src/VBox/Runtime/r3/posix/shmem-posix.cpp
===================================================================
--- /trunk/src/VBox/Runtime/r3/posix/shmem-posix.cpp	(revision 75880)
+++ /trunk/src/VBox/Runtime/r3/posix/shmem-posix.cpp	(revision 75881)
@@ -292,4 +292,6 @@
             if (!pThis->aMappingDescs[i].cMappings)
             {
+                pMappingDesc = &pThis->aMappingDescs[i];
+
                 /* Try to grab this one. */
                 if (ASMAtomicIncU32(&pMappingDesc->cMappings) == 1)
@@ -298,4 +300,5 @@
                 /* Somebody raced us, drop reference and continue. */
                 ASMAtomicDecU32(&pMappingDesc->cMappings);
+                pMappingDesc = NULL;
             }
         }