diff --git a/include/ndn-cpp/c/common.h b/include/ndn-cpp/c/common.h
index 89392bc..c1706d5 100644
--- a/include/ndn-cpp/c/common.h
+++ b/include/ndn-cpp/c/common.h
@@ -12,4 +12,22 @@
 // TODO: Is stddef.h portable?
 #include <stddef.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * A time interval represented as the number of milliseconds.
+ */
+typedef double ndn_Milliseconds;
+   
+/**
+ * The calendar time represented as the number of milliseconds since 1/1/1970.
+ */
+typedef double ndn_MillisecondsSince1970;
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif