diff --git a/stim/image/image.h b/stim/image/image.h
index a7bde6b..6e2925c 100644
--- a/stim/image/image.h
+++ b/stim/image/image.h
@@ -327,7 +327,7 @@ public:
 	void save(std::string filename){
 		stim::filename file(filename);
 		if (file.extension() == "raw" || file.extension() == "") {
-			std::ofstream outfile(filename, std::ios::binary);
+			std::ofstream outfile(filename.c_str(), std::ios::binary);
 			outfile.write((char*)img, sizeof(T) * R[0] * R[1] * R[2]);
 			outfile.close();
 		}
--
libgit2 0.21.4