diff --git a/core/main.mk b/core/main.mk
index 0c70d92..e03d873 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -121,12 +121,20 @@
 $(error Directory names containing spaces not supported)
 endif
 
+# Check for the corrent jdk
+ifneq ($(shell java -version 2>&1 | grep -i openjdk),)
+$(info ************************************************************)
+$(info You are attempting to build with an unsupported JDK.)
+$(info $(space))
+$(info You use OpenJDK but only Sun/Oracle JDK is supported.)
+$(info Please follow the machine setup instructions at)
+$(info $(space)$(space)$(space)$(space)https://source.android.com/source/download.html)
+$(info ************************************************************)
+$(error stop)
+endif
 
 # Check for the correct version of java
 java_version := $(shell java -version 2>&1 | head -n 1 | grep '^java .*[ "]1\.6[\. "$$]')
-ifneq ($(shell java -version 2>&1 | grep -i openjdk),)
-java_version :=
-endif
 ifeq ($(strip $(java_version)),)
 $(info ************************************************************)
 $(info You are attempting to build with the incorrect version)