diff --git a/flash.h b/flash.h
index c1d8980..1a9bd9f 100644
--- a/flash.h
+++ b/flash.h
@@ -314,6 +314,7 @@
 void reverse_bytes(uint8_t *dst, const uint8_t *src, size_t length);
 #ifdef __MINGW32__
 char* strtok_r(char *str, const char *delim, char **nextp);
+char *strndup(const char *str, size_t size);
 #endif
 #if defined(__DJGPP__) || (!defined(__LIBPAYLOAD__) && !defined(HAVE_STRNLEN))
 size_t strnlen(const char *str, size_t n);
diff --git a/helpers.c b/helpers.c
index cfa9812..c83cd2c 100644
--- a/helpers.c
+++ b/helpers.c
@@ -102,6 +102,20 @@
 	*nextp = str;
 	return ret;
 }
+
+/* strndup is a POSIX function not present in MinGW */
+char *strndup(const char *src, size_t maxlen)
+{
+	if (strlen(src) > maxlen) {
+		char *retbuf;
+		if ((retbuf = malloc(1 + maxlen)) != NULL) {
+			memcpy(retbuf, src, maxlen);
+			retbuf[maxlen] = '\0';
+		}
+		return retbuf;
+	}
+	return strdup(src);
+}
 #endif
 
 /* There is no strnlen in DJGPP */