diff --git a/ext/gtest/Makefile.am b/ext/gtest/Makefile.am
index f313ba53e2..f8f8536d7c 100644
--- a/ext/gtest/Makefile.am
+++ b/ext/gtest/Makefile.am
@@ -7,4 +7,4 @@ libgtest_a_CXXFLAGS = $(GTEST_INCLUDES) $(AM_CXXFLAGS)
 nodist_libgtest_a_SOURCES = gtest-all.cc
 
 gtest-all.cc: $(GTEST_SOURCE)/src/gtest-all.cc
-	cp -p $< $@
+	cp -p $(GTEST_SOURCE)/src/gtest-all.cc $@