diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 064e468..9977fff 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -13,5 +13,6 @@ jobs:
     - uses: actions/checkout@v2
     - uses: jiro4989/setup-nim-action@v1
     - run: nimble test -d:release -y
+    - run: nimble test -d:release -d:pixieNoSimd -y
     - run: nimble test --gc:orc -d:release -y
     - run: nim cpp -d:release -r tests/all.nim
diff --git a/src/pixie/images.nim b/src/pixie/images.nim
index f5614a7..b4185b0 100644
--- a/src/pixie/images.nim
+++ b/src/pixie/images.nim
@@ -753,31 +753,32 @@ proc drawUber(a, b: Image | Mask, mat = mat3(), blendMode = bmNormal) =
                 )
                 x += 16
 
-      for _ in x ..< xMax:
-        let
-          srcPos = p + dx * x.float32 + dy * y.float32
-          xFloat = srcPos.x - h
-          yFloat = srcPos.y - h
+      var srcPos = p + dx * x.float32 + dy * y.float32
+      srcPos = vec2(max(0, srcPos.x), max(0, srcPos.y))
+
+      for x in x ..< xMax:
+        let samplePos = ivec2((srcPos.x - h).int32, (srcPos.y - h).int32)
 
         when type(a) is Image:
           let backdrop = a.getRgbaUnsafe(x, y)
           when type(b) is Image:
             let
-              sample = b.getRgbaUnsafe(xFloat.int, yFloat.int)
+              sample = b.getRgbaUnsafe(samplePos.x, samplePos.y)
               blended = blender(backdrop, sample)
           else: # b is a Mask
             let
-              sample = b.getValueUnsafe(xFloat.int, yFloat.int)
+              sample = b.getValueUnsafe(samplePos.x, samplePos.y)
               blended = blender(backdrop, rgbx(0, 0, 0, sample))
           a.setRgbaUnsafe(x, y, blended)
         else: # a is a Mask
           let backdrop = a.getValueUnsafe(x, y)
           when type(b) is Image:
-            let sample = b.getRgbaUnsafe(xFloat.int, yFloat.int).a
+            let sample = b.getRgbaUnsafe(samplePos.x, samplePos.y).a
           else: # b is a Mask
-            let sample = b.getValueUnsafe(xFloat.int, yFloat.int)
+            let sample = b.getValueUnsafe(samplePos.x, samplePos.y)
           a.setValueUnsafe(x, y, masker(backdrop, sample))
-        inc x
+
+        srcPos += dx
 
     if blendMode == bmIntersectMask:
       if a.width - xMax > 0: