diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36a7e80fb..809653a79 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -395,10 +395,6 @@ check_function_exists( setgroups HAVE_SETGROUPS )
 check_function_exists( setlocale HAVE_SETLOCALE )
 check_function_exists( setmntent HAVE_SETMNTENT )
 check_function_exists( setpriority HAVE_SETPRIORITY )
-check_function_exists( isnan HAVE_FUNC_ISNAN )
-check_function_exists( _finite HAVE_FUNC__FINITE )
-check_function_exists( finite HAVE_FUNC_FINITE )
-check_function_exists( isinf HAVE_FUNC_ISINF )
 check_function_exists( freeaddrinfo HAVE_FREEADDRINFO )
 check_function_exists( strtoll HAVE_STRTOLL )
 check_function_exists( socket HAVE_SOCKET )
diff --git a/config.h.cmake b/config.h.cmake
index 5ee6f156b..49b689983 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -212,18 +212,6 @@
 /* Define to 1 if you have the <fstab.h> header file. */
 #cmakedefine HAVE_FSTAB_H 1
 
-/* Define if you have finite */
-#cmakedefine HAVE_FUNC_FINITE 1
-
-/* Define if you have isinf */
-#cmakedefine HAVE_FUNC_ISINF 1
-
-/* Define if you have isnan */
-#cmakedefine HAVE_FUNC_ISNAN 1
-
-/* Define if you have _finite */
-#cmakedefine HAVE_FUNC__FINITE 1
-
 /* Define to 1 if you have the `gai_strerror' function. */
 #cmakedefine HAVE_GAI_STRERROR 1
 
diff --git a/kjs/configure.in.in b/kjs/configure.in.in
index fd23612e0..1c4d3ac52 100644
--- a/kjs/configure.in.in
+++ b/kjs/configure.in.in
@@ -1,46 +1,6 @@
 dnl KDE JavaScript specific configure tests
 
 AC_CHECK_HEADERS(ieeefp.h float.h)
-AC_CHECK_LIB(m, finite, [
-  AC_DEFINE_UNQUOTED(HAVE_FUNC_FINITE, 1, [Define if you have finite])
-])
-AC_CHECK_LIB(m, _finite, [
-  AC_DEFINE_UNQUOTED(HAVE_FUNC__FINITE, 1, [Define if you have _finite])
-])
-
-dnl The C99 standard says that isinf and isnan are macros, but they might
-dnl be functions on some platforms.
-AC_DEFUN([AC_CHECK_ISNAN],
-[
-    ac_save_libs="$LIBS"
-    LIBS="-lm"
-    AC_MSG_CHECKING([for isnan with <math.h>])
-    AC_TRY_LINK(
-	[#include <math.h>
-         float f;], [return isnan(f)],
-	[AC_MSG_RESULT(yes)
-	    AC_DEFINE([HAVE_FUNC_ISNAN], [1], [Define if you have isnan])],
-	AC_MSG_RESULT(no)
-    )
-    LIBS="$ac_save_libs"
-])
-AC_DEFUN([AC_CHECK_ISINF],
-[
-    ac_save_libs="$LIBS"
-    LIBS="-lm"
-    AC_MSG_CHECKING([for isinf with <math.h>])
-    AC_TRY_LINK(
-	[#include <math.h>
-         float f;], [return isinf(f)],
-	[AC_MSG_RESULT(yes)
-	    AC_DEFINE([HAVE_FUNC_ISINF], [1], [Define if you have isinf])],
-	AC_MSG_RESULT(no)
-    )
-    LIBS="$ac_save_libs"
-])
-
-AC_CHECK_ISNAN
-AC_CHECK_ISINF
 
 AC_DEFUN([AC_CHECK_PCREPOSIX],
 [
diff --git a/kjs/operations.cpp b/kjs/operations.cpp
index 63c1e669e..b9314eccb 100644
--- a/kjs/operations.cpp
+++ b/kjs/operations.cpp
@@ -25,7 +25,6 @@
 #endif
 #ifndef HAVE_FLOAT_H   /* just for !Windows */
 #define HAVE_FLOAT_H 0
-#define HAVE_FUNC__FINITE 0
 #endif
 
 #include <stdio.h>
@@ -38,11 +37,9 @@
 #include <sunmath.h>
 #endif
 
-#ifndef HAVE_FUNC_ISINF
 #ifdef HAVE_IEEEFP_H
 #include <ieeefp.h>
 #endif
-#endif /* HAVE_FUNC_ISINF */
 
 #if HAVE_FLOAT_H
 #include <float.h>
@@ -55,52 +52,22 @@ using namespace KJS;
 
 bool KJS::isNaN(double d)
 {
-#ifdef HAVE_FUNC_ISNAN
   return isnan(d);
-#elif defined HAVE_FLOAT_H
-  return _isnan(d) != 0;
-#else
-  return !(d == d);
-#endif
 }
 
 bool KJS::isInf(double d)
 {
-#if defined(HAVE_FUNC_ISINF)
   return isinf(d);
-#elif HAVE_FUNC_FINITE
-  return finite(d) == 0 && d == d;
-#elif HAVE_FUNC__FINITE
-  return _finite(d) == 0 && d == d;
-#else
-  return false;
-#endif
 }
 
 bool KJS::isPosInf(double d)
 {
-#if defined(HAVE_FUNC_ISINF)
-  return (isinf(d) == 1);
-#elif HAVE_FUNC_FINITE
-  return finite(d) == 0 && d == d; // ### can we distinguish between + and - ?
-#elif HAVE_FUNC__FINITE
-  return _finite(d) == 0 && d == d; // ###
-#else
-  return false;
-#endif
+  return ( isinf(d) && d > 0 );
 }
 
 bool KJS::isNegInf(double d)
 {
-#if defined(HAVE_FUNC_ISINF)
-  return (isinf(d) == -1);
-#elif HAVE_FUNC_FINITE
-  return finite(d) == 0 && d == d; // ###
-#elif HAVE_FUNC__FINITE
-  return _finite(d) == 0 && d == d; // ###
-#else
-  return false;
-#endif
+  return ( isinf(d) && d < 0 );
 }
 
 // ECMA 11.9.3