1 files changed, 5 insertions, 0 deletions
diff --git a/lib/sha1.h b/lib/sha1.h
index e867724..07e943f 100644
--- a/lib/sha1.h
+++ b/lib/sha1.h
@@ -5,6 +5,9 @@
 * https://opensource.org/licenses/MIT
 ***/
 
+#ifndef SHA1DC_SHA1_H
+#define SHA1DC_SHA1_H
+
 #if defined(__cplusplus)
 extern "C" {
 #endif
@@ -103,3 +106,5 @@ int  SHA1DCFinal(unsigned char[20], SHA1_CTX*);
 #if defined(__cplusplus)
 }
 #endif
+
+#endif