diff --git a/content/canvas/src/nsCanvasRenderingContext2D.cpp b/content/canvas/src/nsCanvasRenderingContext2D.cpp
index b2e0e50d3ba..a65aebe1819 100644
--- a/content/canvas/src/nsCanvasRenderingContext2D.cpp
+++ b/content/canvas/src/nsCanvasRenderingContext2D.cpp
@@ -3520,7 +3520,7 @@ nsCanvasRenderingContext2D::DrawImage(nsIDOMElement *imgElt, float a1,
         DirtyAllStyles();
 
         /* Direct2D isn't very good at clipping so use Fill() when we can */
-        if (CurrentState().globalAlpha = 1. && mThebes->CurrentOperator() == gfxContext::OPERATOR_OVER) {
+        if (CurrentState().globalAlpha == 1.0f && mThebes->CurrentOperator() == gfxContext::OPERATOR_OVER) {
             mThebes->Rectangle(clip);
             mThebes->Fill();
         } else {