diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index 3ef4e2e3e..5820f11df 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -343,10 +343,12 @@ GLHorizonPortal::GLHorizonPortal(FPortalSceneState *s, GLHorizonInfo * pt, FRend
 	// Draw to some far away boundary
 	// This is not drawn as larger strips because it causes visual glitches.
 	FFlatVertex *ptr = GLRenderer->mVBO->GetBuffer();
-	for (float x = -32768 + vx; x<32768 + vx; x += 4096)
+	for (int xx = -32768; xx < 32768; xx += 4096)
 	{
-		for (float y = -32768 + vy; y<32768 + vy; y += 4096)
+		float x = xx + vx;
+		for (int yy = -32768; yy < 32768; yy += 4096)
 		{
+			float y = yy + vy;
 			ptr->Set(x, z, y, x / 64, -y / 64);
 			ptr++;
 			ptr->Set(x + 4096, z, y, x / 64 + 64, -y / 64);