diff --git a/core/main.mk b/core/main.mk
index ec5721e..0ef05f1 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -151,8 +151,8 @@
 endif
 endif
 
-java_version_str := $(shell java -version 2>&1)
-javac_version_str := $(shell javac -version 2>&1)
+java_version_str := $(shell unset _JAVA_OPTIONS && java -version 2>&1)
+javac_version_str := $(shell unset _JAVA_OPTIONS && javac -version 2>&1)
 
 # Check for the current jdk
 ifeq ($(requires_openjdk), true)
@@ -187,13 +187,13 @@
 ifneq ($(EXPERIMENTAL_USE_JAVA7),)
 required_version := "1.7.x"
 required_javac_version := "1.7"
-java_version := $(shell echo '$(java_version_str)' | grep '^java .*[ "]1\.7[\. "$$]' | head -n 1)
-javac_version := $(shell echo '$(javac_version_str)' | grep '[ "]1\.7[\. "$$]' | head -n 1)
+java_version := $(shell echo '$(java_version_str)' | grep '^java .*[ "]1\.7[\. "$$]')
+javac_version := $(shell echo '$(javac_version_str)' | grep '[ "]1\.7[\. "$$]')
 else # if EXPERIMENTAL_USE_JAVA7
 required_version := "1.6.x"
 required_javac_version := "1.6"
-java_version := $(shell echo '$(java_version_str)' | grep '^java .*[ "]1\.6[\. "$$]' | head -n 1)
-javac_version := $(shell echo '$(javac_version_str)' | head -n 1 | grep '[ "]1\.6[\. "$$]' | head -n 1)
+java_version := $(shell echo '$(java_version_str)' | grep '^java .*[ "]1\.6[\. "$$]')
+javac_version := $(shell echo '$(javac_version_str)' | grep '[ "]1\.6[\. "$$]')
 endif # if EXPERIMENTAL_USE_JAVA7
 
 ifeq ($(required_javac_version), "1.6")