--- a/make/Defs-internal.gmk	Thu Mar 13 16:12:15 2008 -0700
+++ b/make/Defs-internal.gmk	Tue Mar 18 11:01:40 2008 -0700
@@ -27,6 +27,12 @@
 # Common variables used by all the Java makefiles.  This file should
 # not contain rules.
 #
+
+ifdef OPENJDK
+  ifneq ($(OPENJDK),true)
+    x:=$(error "OPENJDK (if defined) can only be set to true")
+  endif
+endif
 
 # Define absolute paths to TOPDIRs
 ABS_CONTROL_TOPDIR:=$(call OptFullPath,"$(CONTROL_TOPDIR)")
@@ -96,10 +102,8 @@ endif
 endif
 ifeq ($(JDK_SRC_AVAILABLE),true)
   JDK_CLOSED_SRC_AVAILABLE := $(call MkExists,$(JDK_TOPDIR)/src/closed)
-  ifndef OPENJDK
-    ifeq ($(JDK_CLOSED_SRC_AVAILABLE),false)
-      OPENJDK = true
-    endif
+  ifeq ($(JDK_CLOSED_SRC_AVAILABLE),false)
+    OPENJDK = true
   endif
 endif