diff --git a/src/geom/ofxFlashMatrix.h b/src/geom/ofxFlashMatrix.h
index d604601..74eff0e 100644
--- a/src/geom/ofxFlashMatrix.h
+++ b/src/geom/ofxFlashMatrix.h
@@ -230,7 +230,7 @@ class ofxFlashMatrix : public ofMatrix4x4
 	{
 		const float rot_y = atan2( -getC(), getD() );
 		
-		setC( yscale * sin( rot_y ) );
+		setC( yscale * -sin( rot_y ) );
 		setD( yscale * cos( rot_y ) );
 	}