diff --git a/src/pem.c b/src/pem.c
index 3e496fe..9f51bba 100644
--- a/src/pem.c
+++ b/src/pem.c
@@ -89,7 +89,7 @@ readline_memory(char *line, size_t line_size,
     }
 
     line[len] = '\0';
-    *filedata_offset++;
+    *filedata_offset += 1;
 
     return 0;
 }