diff --git a/src/filesystem/simple_fs_nix.cpp b/src/filesystem/simple_fs_nix.cpp
index bb2808462..25e604dbf 100644
--- a/src/filesystem/simple_fs_nix.cpp
+++ b/src/filesystem/simple_fs_nix.cpp
@@ -217,7 +217,7 @@ std::vector<unopened_file> list_files(directory const& dir, native_char const* e
 						continue;
 
 					// Check if the file is of the right extension
-					if(strlen(extension)) {
+					if(extension && extension[0] != 0) {
 						char* dot = strrchr(dir_ent->d_name, '.');
 						if(!dot || dot == dir_ent->d_name)
 							continue;
@@ -249,7 +249,7 @@ std::vector<unopened_file> list_files(directory const& dir, native_char const* e
 					continue;
 
 				// Check if the file is of the right extension
-				if(strlen(extension)) {
+				if(extension && extension[0] != 0) {
 					char* dot = strrchr(dir_ent->d_name, '.');
 					if(!dot || dot == dir_ent->d_name)
 						continue;