diff --git a/gfx/ycbcr/yuv_convert.cpp b/gfx/ycbcr/yuv_convert.cpp
--- a/gfx/ycbcr/yuv_convert.cpp
+++ b/gfx/ycbcr/yuv_convert.cpp
@@ -337,16 +337,17 @@ NS_GFX_(void) ScaleYCbCrToRGB32(const ui
                                          source_dx_uv >> kFractionBits);
         }
       }
       else {
         ScaleYUVToRGB32Row_C(y_ptr, u_ptr, v_ptr,
                              dest_pixel, width, source_dx);
       }
 #else
+      (void)source_dx_uv;
       ScaleYUVToRGB32Row(y_ptr, u_ptr, v_ptr,
                          dest_pixel, width, source_dx);
 #endif
     }
   }
   // MMX used for FastConvertYUVToRGB32Row and FilterRows requires emms.
   if (has_mmx)
     EMMS();
diff --git a/gfx/ycbcr/yuv_row.h b/gfx/ycbcr/yuv_row.h
--- a/gfx/ycbcr/yuv_row.h
+++ b/gfx/ycbcr/yuv_row.h
@@ -129,14 +129,14 @@ extern SIMD_ALIGNED(int16 kCoefficientsR
 #if defined(ARCH_CPU_X86) && !defined(ARCH_CPU_X86_64)
 #if defined(_MSC_VER)
 #define EMMS() __asm emms
 #pragma warning(disable: 4799)
 #else
 #define EMMS() asm("emms")
 #endif
 #else
-#define EMMS()
+#define EMMS() ((void)0)
 #endif
 
 }  // extern "C"
 
 #endif  // MEDIA_BASE_YUV_ROW_H_