diff --git a/ext/date/date_parse.c b/ext/date/date_parse.c
index c6f26ecb91..a1600e4708 100644
--- a/ext/date/date_parse.c
+++ b/ext/date/date_parse.c
@@ -7,6 +7,9 @@
 #include "ruby/re.h"
 #include <ctype.h>
 
+#undef strncasecmp
+#define strncasecmp STRNCASECMP
+
 RUBY_EXTERN VALUE rb_int_positive_pow(long x, unsigned long y);
 RUBY_EXTERN unsigned long ruby_scan_digits(const char *str, ssize_t len, int base, size_t *retlen, int *overflow);
 
diff --git a/ext/date/date_strptime.c b/ext/date/date_strptime.c
index f731629df1..da58c21a76 100644
--- a/ext/date/date_strptime.c
+++ b/ext/date/date_strptime.c
@@ -7,6 +7,9 @@
 #include "ruby/re.h"
 #include <ctype.h>
 
+#undef strncasecmp
+#define strncasecmp STRNCASECMP
+
 static const char *day_names[] = {
     "Sunday", "Monday", "Tuesday", "Wednesday",
     "Thursday", "Friday", "Saturday",