diff --git a/common/gal/color4d.cpp b/common/gal/color4d.cpp
index e4ed67d749..09b04f8929 100644
--- a/common/gal/color4d.cpp
+++ b/common/gal/color4d.cpp
@@ -510,7 +510,7 @@ const COLOR4D COLOR4D::BLACK( 0, 0, 0, 1 );
 const COLOR4D COLOR4D::CLEAR( 1, 0, 1, 0 );
 
 
-int COLOR4D::Distance( const COLOR4D& other ) const
+double COLOR4D::Distance( const COLOR4D& other ) const
 {
     return ( r - other.r ) * ( r - other.r )
             + ( g - other.g ) * ( g - other.g )
diff --git a/include/gal/color4d.h b/include/gal/color4d.h
index 7d91ad77a4..7baf4813b9 100644
--- a/include/gal/color4d.h
+++ b/include/gal/color4d.h
@@ -373,7 +373,7 @@ public:
     /**
      * Returns the distance (in RGB space) between two colors.
      */
-    int Distance( const COLOR4D& other ) const;
+    double Distance( const COLOR4D& other ) const;
 
     /**
      * Returns a legacy color ID that is closest to the given 8-bit RGB values.