diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 52f157c6e..fe0412699 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -2904,7 +2904,12 @@ AstNode *AstNode::readmem(bool is_readmemh, std::string mem_filename, AstNode *m
 	std::ifstream f;
 	f.open(mem_filename.c_str());
 	if (f.fail()) {
-		std::string path = filename.substr(0, filename.find_last_of("\\/")+1);
+#ifdef _WIN32
+		char slash = '\\';
+#else
+		char slash = '/';
+#endif
+		std::string path = filename.substr(0, filename.find_last_of(slash)+1);
 		f.open(path + mem_filename.c_str());
 		yosys_input_files.insert(path + mem_filename);
 	} else {