diff --git a/cygwin/GNUmakefile.in b/cygwin/GNUmakefile.in
index 3cf98487eb..90a35894e3 100644
--- a/cygwin/GNUmakefile.in
+++ b/cygwin/GNUmakefile.in
@@ -2,7 +2,7 @@ gnumake = yes
 
 include Makefile
 
-MUNICODE_FLAG = $(if $(filter mingw%,$(target_os)),-municode)
+MUNICODE_FLAG := $(if $(filter mingw%,$(target_os)),-municode)
 override EXE_LDFLAGS += $(MUNICODE_FLAG)
 
 ENABLE_SHARED=@ENABLE_SHARED@