diff --git a/ndn-cpp/c/common.h b/ndn-cpp/c/common.h
index 23a604c..7f60950 100644
--- a/ndn-cpp/c/common.h
+++ b/ndn-cpp/c/common.h
@@ -19,6 +19,17 @@
 typedef unsigned char uint8_t;
 #endif
 
+#if HAVE_MEMCMP || HAVE_MEMCPY || HAVE_MEMSET
+// size_t is defined in memory.h, or something it includes.
+#include <memory.h>
+#else
+// Need to define size_t.
+#ifndef	_SIZE_T
+#define	_SIZE_T
+typedef	unsigned int size_t;
+#endif
+#endif
+
 #ifdef	__cplusplus
 extern "C" {
 #endif