diff --git a/mk/lib.mk b/mk/lib.mk
index bb82801d..1da51d87 100644
--- a/mk/lib.mk
+++ b/mk/lib.mk
@@ -53,8 +53,8 @@ BUILD_SHARED_LIBS ?= 1
 
 ifeq ($(BUILD_SHARED_LIBS), 1)
   ifeq (CYGWIN,$(findstring CYGWIN,$(OS)))
-    GLOBAL_CFLAGS += -U__STRICT_ANSI__
-    GLOBAL_CXXFLAGS += -U__STRICT_ANSI__
+    GLOBAL_CFLAGS += -U__STRICT_ANSI__ -D_GNU_SOURCE
+    GLOBAL_CXXFLAGS += -U__STRICT_ANSI__ -D_GNU_SOURCE
   else
     GLOBAL_CFLAGS += -fPIC
     GLOBAL_CXXFLAGS += -fPIC