diff --git a/lib/hashes.js b/lib/hashes.js
index 9780e098..21ea5993 100644
--- a/lib/hashes.js
+++ b/lib/hashes.js
@@ -29,22 +29,19 @@ module.exports.compare = async (password, hash) => {
     password = (password || '').toString();
     hash = (hash || '').toString();
 
-    let algo = [].concat(hash.match(/^\$([^$]+)\$/) || [])[1];
-    algo = (algo || '').toString().toLowerCase();
+    let algo = checkHashSupport(hash);
+    if (!algo.result) {
+        throw new Error('Invalid algo: ' + JSON.stringify(algo.algo));
+    }
 
-    switch (algo) {
-        case 'pbkdf2-sha512':
-        case 'pbkdf2-sha256':
-        case 'pbkdf2-sha1':
+    switch (algo.algo) {
+        case 'pbkdf2':
             return await pbkdf2.verify(hash, password);
-
-        case '2a':
-        case '2b':
-        case '2y':
+        case 'bcrypt':
             return await bcrypt.compare(password, hash);
-        case '6':
+        case 'unixcrypt':
             return await unixcryptCompareAsync(password, hash);
-        case '1': {
+        case 'md5': {
             let result;
 
             let salt = hash.split('$')[2] || '';
@@ -57,6 +54,33 @@ module.exports.compare = async (password, hash) => {
     }
 };
 
+function checkHashSupport(hash) {
+    hash = (hash || '').toString();
+
+    let algo = [].concat(hash.match(/^\$([^$]+)\$/) || [])[1];
+    algo = (algo || '').toString().toLowerCase();
+
+    switch (algo) {
+        case 'pbkdf2-sha512':
+        case 'pbkdf2-sha256':
+        case 'pbkdf2-sha1':
+            return { result: true, algo: 'pbkdf2' };
+        case '2a':
+        case '2b':
+        case '2y':
+            return { result: true, algo: 'bcrypt' };
+        case '6':
+            return { result: true, algo: 'unixcrypt' };
+        case '1': {
+            return { result: true, algo: 'md5' };
+        }
+        default:
+            return { result: false, algo };
+    }
+};
+
+module.exports.checkHashSupport = checkHashSupport;
+
 module.exports.shouldRehash = hash => {
     hash = (hash || '').toString();
     let algo = [].concat(hash.match(/^\$([^$]+)\$/) || [])[1];
diff --git a/lib/user-handler.js b/lib/user-handler.js
index 398026dc..3aabe89d 100644
--- a/lib/user-handler.js
+++ b/lib/user-handler.js
@@ -1266,9 +1266,13 @@ class UserHandler {
             try {
                 if (data.hashedPassword) {
                     // try if the hashing library can handle it?
-                    await hashes.compare('whatever', data.password);
-                    // did not throw, so probably OK
-                    hash = data.password;
+                    let algo = hashes.checkHashSupport(data.password);
+                    if (algo.result) {
+                        hash = data.password;
+                    } else {
+                        throw new Error('Invalid algo: ' + JSON.stringify(algo.algo));
+                    }
+
                 } else {
                     hash = await hashes.hash(data.password);
                 }