diff --git a/lib/std/encoding/base64.c3 b/lib/std/encoding/base64.c3
index 67b3cc355..7da874832 100644
--- a/lib/std/encoding/base64.c3
+++ b/lib/std/encoding/base64.c3
@@ -20,59 +20,55 @@ fn char[]! decode_buffer(char[] code, char[] buffer)
 	return buffer[:std_decoder.decode(code, buffer)!];
 }
 
-fn String encode(char[] code, Allocator allocator)
+fn String! encode(char[] code, Allocator allocator)
 {
 	@check_coder(std_encoder);
 	char[] data = allocator::alloc_array(allocator, char, std_encoder.encode_len(code.len));
-	std_encoder.encode(code, data)!!;
-	return (String)data;
+	return (String)data[:std_encoder.encode(code, data)!];
 }
 
 fn char[]! decode(char[] code, Allocator allocator)
 {
 	@check_coder(std_decoder);
 	char[] data = allocator::alloc_array(allocator, char, std_decoder.decode_len(code.len))!;
-	std_decoder.decode(code, data)!;
-	return data;
+	return data[:std_decoder.decode(code, data)!];
 }
 
-fn String encode_new(char[] code) @inline => encode(code, allocator::heap());
-fn String encode_temp(char[] code) @inline => encode(code, allocator::temp());
+fn String! encode_new(char[] code) @inline => encode(code, allocator::heap());
+fn String! encode_temp(char[] code) @inline => encode(code, allocator::temp());
 fn char[]! decode_new(char[] code) @inline => decode(code, allocator::heap());
 fn char[]! decode_temp(char[] code) @inline => decode(code, allocator::temp());
 
-fn String urlencode(char[] code, Allocator allocator)
+fn String! urlencode(char[] code, Allocator allocator)
 {
-	@check_coder(url_encoder);
+	@check_coder(url_encoder, URL_ALPHABET);
 	char[] data = allocator::alloc_array(allocator, char, url_encoder.encode_len(code.len));
-	url_encoder.encode(code, data)!!;
-	return (String)data;
+	return (String)data[:url_encoder.encode(code, data)!];
 }
 
 fn char[]! urldecode(char[] code, Allocator allocator)
 {
-	@check_coder(url_decoder);
+	@check_coder(url_decoder, URL_ALPHABET);
 	char[] data = allocator::alloc_array(allocator, char, url_decoder.decode_len(code.len))!;
-	url_decoder.decode(code, data)!;
-	return data;
+	return data[:url_decoder.decode(code, data)!];
 }
 
 fn String! urlencode_buffer(char[] code, char[] buffer)
 {
-	@check_coder(url_encoder);
-	return (String)buffer[:std_encoder.encode(code, buffer)!];
+	@check_coder(url_encoder, URL_ALPHABET);
+	return (String)buffer[:url_encoder.encode(code, buffer)!];
 }
 
 fn char[]! urldecode_buffer(char[] code, char[] buffer)
 {
-	@check_coder(url_decoder);
+	@check_coder(url_decoder, URL_ALPHABET);
 	return buffer[:url_decoder.decode(code, buffer)!];
 }
 
 fn String! urlencode_new(char[] code) @inline => urlencode(code, allocator::heap());
 fn String! urlencode_temp(char[] code) @inline => urlencode(code, allocator::temp());
-fn char[]! urldecode_new(char[] code) @inline => decode(code, allocator::heap());
-fn char[]! urldecode_temp(char[] code) @inline => decode(code, allocator::temp());
+fn char[]! urldecode_new(char[] code) @inline => urldecode(code, allocator::heap());
+fn char[]! urldecode_temp(char[] code) @inline => urldecode(code, allocator::temp());
 
 
 const MASK @private = 0b111111;
@@ -347,8 +343,8 @@ tlocal Base64Decoder std_decoder @local;
 tlocal Base64Decoder url_decoder @local;
 
 
-macro @check_coder(#coder) @local
+macro @check_coder(#coder, alphabet = STD_ALPHABET) @local
 {
-	if (#coder.alphabet) return;
-	#coder.init(STD_ALPHABET, '=')!!;
-}
\ No newline at end of file
+	if (#coder.alphabet == alphabet) return;
+	#coder.init(alphabet, '=')!!;
+}
diff --git a/test/unit/stdlib/encoding/base64.c3 b/test/unit/stdlib/encoding/base64.c3
index f9b56f274..f03499f99 100644
--- a/test/unit/stdlib/encoding/base64.c3
+++ b/test/unit/stdlib/encoding/base64.c3
@@ -31,7 +31,7 @@ fn void encode()
             char[64] buf;
             b.encode(tc.in, buf[:n])!;
             assert(buf[:n] == tc.out);
-            assert(base64::encode_temp(tc.in) == tc.out);
+            assert(base64::encode_temp(tc.in)! == tc.out);
         };
     }
 }
@@ -105,3 +105,34 @@ fn void decode_nopadding()
         assert(buf[:nn] == tc.out);
     }
 }
+
+fn void! urlencode() {
+	TestCase[] tcases = {
+		{ x"14fb9c03d97e", "FPucA9l-"},
+	};
+
+	@pool()
+	{
+		usz n;
+		char[] got;
+		char[64] buf;
+		foreach (t : tcases)
+		{
+			Base64Encoder enc;
+			enc.init(base64::URL_ALPHABET)!;
+			n = enc.encode(t.in, buf[..])!;
+			assert (buf[:n] == t.out, "got: %s, want: %s", (String)buf[:n], (String)t.out);
+
+			got = base64::urlencode_temp(t.in)!;
+			assert (got == t.out, "got: %s, want: %s", got, (String)t.out);
+
+			Base64Decoder dec;
+			dec.init(base64::URL_ALPHABET)!;
+			n = dec.decode(t.out, buf[..])!;
+			assert (buf[:n] == t.in, "got: %s, want: %s", (String)buf[:n], (String)t.in);
+
+			got = base64::urldecode_temp(t.out)!;
+			assert (got == t.in, "got: %s, want: %s", got, (String)t.in);
+		}
+	};
+}