diff --git a/common_func.c b/common_func.c
index 04b666ed..a8093b34 100644
--- a/common_func.c
+++ b/common_func.c
@@ -92,8 +92,10 @@ char* str_tolower(const char* str)
  */
 char* str_trim(char* str)
 {
-	char* last = str + strlen(str) - 1;
+	char* last;
 	while (isspace((unsigned char)*str)) str++;
+	if (!*str) return str;
+	last = str + strlen(str) - 1;
 	while (isspace((unsigned char)*last) && last > str) *(last--) = 0;
 	return str;
 }
diff --git a/tests/test_empty_config_name.py b/tests/test_empty_config_name.py
new file mode 100644
index 00000000..ee45aaed
--- /dev/null
+++ b/tests/test_empty_config_name.py
@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+from pathlib import Path
+import os
+import subprocess
+import sys
+import tempfile
+
+binary = str(Path(sys.argv[1]).resolve())
+with tempfile.TemporaryDirectory() as directory:
+    config = Path(directory, "rhash", "rhashrc")
+    config.parent.mkdir()
+    config.write_text("=ignored\nsha256=on\n")
+    env = dict(os.environ, XDG_CONFIG_HOME=directory)
+    result = subprocess.run([binary, "--message=abc"], env=env,
+                            capture_output=True, text=True, timeout=10)
+    assert result.returncode == 0, (result.returncode, result.stderr)
+    assert "unknown option" in result.stderr, result.stderr
+    assert "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad" in result.stdout, result.stdout
+print("PASS: empty configuration name warns and subsequent SHA-256 option works")