diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 310f6fc32..1b6618cd8 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -2886,15 +2886,15 @@ AstNode *AstNode::readmem(bool is_readmemh, std::string mem_filename, AstNode *m
 	int meminit_size=0;
 
 	std::ifstream f;
-	std::string path = filename.substr(0, filename.find_last_of("\\/")+1);
 	f.open(mem_filename.c_str());
 	if (f.fail()) {
+		std::string path = filename.substr(0, filename.find_last_of("\\/")+1);
 		f.open(path + mem_filename.c_str());
 		yosys_input_files.insert(path + mem_filename);
 	} else {
 		yosys_input_files.insert(mem_filename);
 	}
-	if (f.fail() || strlen(mem_filename.c_str()) == 0)
+	if (f.fail() || GetSize(mem_filename) == 0)
 		log_file_error(filename, linenum, "Can not open file `%s` for %s.\n", mem_filename.c_str(), str.c_str());
 
 	log_assert(GetSize(memory->children) == 2 && memory->children[1]->type == AST_RANGE && memory->children[1]->range_valid);