diff --git a/defs/gmake.mk b/defs/gmake.mk
index 0a60a83c14..c6fdbca969 100644
--- a/defs/gmake.mk
+++ b/defs/gmake.mk
@@ -291,8 +291,8 @@ $(UNICODE_SRC_DATA_DIR)/.unicode-tables.time: \
 	$(UNICODE_FILES) $(UNICODE_PROPERTY_FILES)
 endif
 
-REVISION_IN_HEADER := $(shell sed -n 's/^\#define RUBY_FULL_REVISION "\(.*\)"/\1/p' $(srcdir)/revision.h)
-REVISION_LATEST := $(shell git -C $(srcdir) log -1 --format=%H)
+REVISION_IN_HEADER := $(shell sed -n 's/^\#define RUBY_FULL_REVISION "\(.*\)"/\1/p' $(srcdir)/revision.h 2>/dev/null)
+REVISION_LATEST := $(shell cd $(srcdir) && git log -1 --format=%H)
 ifneq ($(REVISION_IN_HEADER),$(REVISION_LATEST))
 # GNU make treat the target as unmodified when its dependents get
 # updated but it is not updated, while others may not.