diff --git a/src/util/unicode.test.c b/src/util/unicode.test.c
index e16ec7f96..6eb3c4c52 100644
--- a/src/util/unicode.test.c
+++ b/src/util/unicode.test.c
@@ -29,7 +29,7 @@ static void test_unicode_trim(CuTest * tc)
     CuAssertIntEquals(tc, 3, unicode_utf8_trim(buffer));
     CuAssertStrEquals(tc, "Hello Word", buffer);
 
-    buffer[9] = 0xc3;
+    buffer[9] = (char)0xc3;
     CuAssertIntEquals(tc, 1, unicode_utf8_trim(buffer));
     CuAssertStrEquals(tc, "Hello Wor?", buffer);
 }