diff --git a/classes/tdesktop.cc b/classes/tdesktop.cc
index 38f1be4..f8f44f0 100644
--- a/classes/tdesktop.cc
+++ b/classes/tdesktop.cc
@@ -26,6 +26,10 @@ Modified cursor behavior while desktop locked by Salvador E. Tropea (SET)
 #define Uses_TVCodePage
 #include <tv.h>
 
+#include <cmath>
+
+using std::abs;
+
 TDeskInit::TDeskInit( TBackground *(*cBackground)( TRect ) ) :
     createBackground( cBackground )
 {
diff --git a/classes/tdisplay.cc b/classes/tdisplay.cc
index 9225d48..ee5eca8 100644
--- a/classes/tdisplay.cc
+++ b/classes/tdisplay.cc
@@ -22,6 +22,10 @@ same used in original Turbo Vision for compatibility purposes.
 #define Uses_TVCodePage
 #include <tv.h>
 
+#include <cmath>
+
+using std::abs;
+
 // Remove me please!
 int TDisplay::dual_display=0;
 
diff --git a/classes/x11/x11src.cc b/classes/x11/x11src.cc
index 538457e..10f9911 100644
--- a/classes/x11/x11src.cc
+++ b/classes/x11/x11src.cc
@@ -98,6 +98,10 @@
  #define TIMER_ALARM SIGALRM
 #endif
 
+#include <cmath>
+
+using std::abs;
+
 const unsigned foWmin=5, foHmin=7, foWmax=20, foHmax=32;
 const int cursorDelay=300000;