diff --git a/tests/JpegTest.cpp b/tests/JpegTest.cpp
index b0c76fc..7a5ee4d 100644
--- a/tests/JpegTest.cpp
+++ b/tests/JpegTest.cpp
@@ -19,7 +19,7 @@
                                                  // normal unit testing.
 
 namespace {
-    char goodJpegImage[] = {
+    unsigned char goodJpegImage[] = {
         0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 0x4A, 0x46,
         0x49, 0x46, 0x00, 0x01, 0x01, 0x01, 0x00, 0x8F,
         0x00, 0x8F, 0x00, 0x00, 0xFF, 0xDB, 0x00, 0x43,