diff --git a/src/gtk/dcclient.cpp b/src/gtk/dcclient.cpp
index 1e91d4b048..d68a6746ee 100644
--- a/src/gtk/dcclient.cpp
+++ b/src/gtk/dcclient.cpp
@@ -14,7 +14,7 @@
 #include "wx/dcclient.h"
 #include "wx/dcmemory.h"
 #include "wx/image.h"
-#include <math.h>
+#include <math.h>               // for floating-point functions
 
 #include "gdk/gdk.h"
 #include "gtk/gtk.h"
@@ -874,7 +874,9 @@ void wxWindowDC::SetPen( const wxPen &pen )
     {
         // X doesn't allow different width in x and y and so we take
         // the average
-        double w = 0.5 + (abs((double) XLOG2DEVREL(width)) + abs((double) YL2DEVREL(width))) / 2.0;
+        double w = 0.5 +
+                   ( fabs((double) XLOG2DEVREL(width)) +
+                     fabs((double) YLOG2DEVREL(width)) ) / 2.0;
         width = (int)w;
     }
   
diff --git a/src/gtk1/dcclient.cpp b/src/gtk1/dcclient.cpp
index 1e91d4b048..d68a6746ee 100644
--- a/src/gtk1/dcclient.cpp
+++ b/src/gtk1/dcclient.cpp
@@ -14,7 +14,7 @@
 #include "wx/dcclient.h"
 #include "wx/dcmemory.h"
 #include "wx/image.h"
-#include <math.h>
+#include <math.h>               // for floating-point functions
 
 #include "gdk/gdk.h"
 #include "gtk/gtk.h"
@@ -874,7 +874,9 @@ void wxWindowDC::SetPen( const wxPen &pen )
     {
         // X doesn't allow different width in x and y and so we take
         // the average
-        double w = 0.5 + (abs((double) XLOG2DEVREL(width)) + abs((double) YL2DEVREL(width))) / 2.0;
+        double w = 0.5 +
+                   ( fabs((double) XLOG2DEVREL(width)) +
+                     fabs((double) YLOG2DEVREL(width)) ) / 2.0;
         width = (int)w;
     }