diff --git a/lib/std/mem.zig b/lib/std/mem.zig
index 46f23c84fe802d7c81f9791884a0f7ee722bea2b..8f4987e0c94ed7f4ab48fd09291e1f8d7b3101fb 100644
--- a/lib/std/mem.zig
+++ b/lib/std/mem.zig
@@ -233,7 +233,7 @@ pub const Allocator = struct {
     pub fn free(self: *Allocator, memory: var) void {
         const Slice = @typeInfo(@TypeOf(memory)).Pointer;
         const bytes = @sliceToBytes(memory);
-        const bytes_len = bytes.len + @boolToInt(Slice.sentinel != null);
+        const bytes_len = bytes.len + if (Slice.sentinel != null) @sizeOf(Slice.child) else 0;
         if (bytes_len == 0) return;
         const non_const_ptr = @intToPtr([*]u8, @ptrToInt(bytes.ptr));
         @memset(non_const_ptr, undefined, bytes_len);
diff --git a/lib/std/unicode.zig b/lib/std/unicode.zig
index 77783c3eddac3f55889c164cd8189d5c79a512ae..da0dbc3cb24da2894955476bda40eeba8aab858a 100644
--- a/lib/std/unicode.zig
+++ b/lib/std/unicode.zig
@@ -571,8 +571,9 @@ pub fn utf8ToUtf16LeWithNull(allocator: *mem.Allocator, utf8: []const u8) ![:0]u
         }
     }
 
+    const len = result.len;
     try result.append(0);
-    return result.toOwnedSlice()[0..:0];
+    return result.toOwnedSlice()[0..len :0];
 }
 
 /// Returns index of next character. If exact fit, returned index equals output slice length.
@@ -619,12 +620,14 @@ test "utf8ToUtf16LeWithNull" {
         var bytes: [128]u8 = undefined;
         const allocator = &std.heap.FixedBufferAllocator.init(bytes[0..]).allocator;
         const utf16 = try utf8ToUtf16LeWithNull(allocator, "𐐷");
-        testing.expectEqualSlices(u8, "\x01\xd8\x37\xdc\x00\x00", @sliceToBytes(utf16[0..]));
+        testing.expectEqualSlices(u8, "\x01\xd8\x37\xdc", @sliceToBytes(utf16[0..]));
+        testing.expect(utf16[2] == 0);
     }
     {
         var bytes: [128]u8 = undefined;
         const allocator = &std.heap.FixedBufferAllocator.init(bytes[0..]).allocator;
         const utf16 = try utf8ToUtf16LeWithNull(allocator, "\u{10FFFF}");
-        testing.expectEqualSlices(u8, "\xff\xdb\xff\xdf\x00\x00", @sliceToBytes(utf16[0..]));
+        testing.expectEqualSlices(u8, "\xff\xdb\xff\xdf", @sliceToBytes(utf16[0..]));
+        testing.expect(utf16[2] == 0);
     }
 }