diff --git a/ChangeLog b/ChangeLog
index bad5914..51a4f89 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2005-04-24  Richard B. Kreckel  <kreckel@ginac.de>
+
+	Make GCC compiler flags default to -O
+	* m4/cc.m4: New file...
+	* configure.ac: ...used here.
+	* autoconf/aclocal.m4: Regenerate.
+
 2005-04-18  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
 
 	* include/cln/string.h: Declare cl_string.
diff --git a/autoconf/aclocal.m4 b/autoconf/aclocal.m4
index 388b458..8f92295 100644
--- a/autoconf/aclocal.m4
+++ b/autoconf/aclocal.m4
@@ -868,5 +868,6 @@ fi
 fi
 ])
 
+m4_include([m4/cc.m4])
 m4_include([m4/gmp.m4])
 m4_include([m4/libtool.m4])
diff --git a/configure.ac b/configure.ac
index c7c966f..bd77b6d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -41,11 +41,11 @@ d
 dnl
 dnl           checks for programs
 dnl
-AC_PROG_CC
+CL_PROG_CC
                       dnl sets variable CC
 AC_PROG_CPP
                       dnl sets variable CPP
-AC_PROG_CXX
+CL_PROG_CXX
                       dnl sets variable CXX
 AC_PROG_CXXCPP
                       dnl sets variable CXXCPP
diff --git a/m4/cc.m4 b/m4/cc.m4
new file mode 100644
index 0000000..a18c47d
--- /dev/null
+++ b/m4/cc.m4
@@ -0,0 +1,33 @@
+dnl The CLN manual says that without CFLAGS or CXXFLAGS being set compilation
+dnl will happen with -O.  However, AC_PROG_CC and AC_PROG_CXX set CFLAGS and
+dnl CXXFLAGS to "-g -O2", which produces way too large binaries.
+
+
+dnl Wrapper around AC_PROG_CC setting CFLAGS to plain "-O" as opposed to
+dnl "-g -O2" for the GNU compiler (unless CFLAGS was set before).
+AC_DEFUN([CL_PROG_CC],
+[cl_test_CFLAGS=${CFLAGS+set}
+cl_save_CFLAGS=$CFLAGS
+# Make sure this macro does not come after AC_PROG_CC.
+# Otherwise CFLAGS would already be set.
+AC_BEFORE([$0],[AC_PROG_CC])dnl
+AC_PROG_CC([$1])
+if test "$cl_test_CFLAGS" != set && test "$ac_compiler_gnu" = yes; then
+    CFLAGS="-O"
+fi
+])
+
+
+dnl Wrapper around AC_PROG_CXX setting CXXFLAGS to plain "-O" as opposed to
+dnl "-g -O2" for the GNU compiler (unless CXXFLAGS was set before).
+AC_DEFUN([CL_PROG_CXX],
+[cl_test_CXXFLAGS=${CXXFLAGS+set}
+cl_save_CXXFLAGS=$CXXFLAGS
+# Make sure this macro does not come after AC_PROG_CXX.
+# Otherwise CXXFLAGS would already be set.
+AC_BEFORE([$0],[AC_PROG_CXX])dnl
+AC_PROG_CXX([$1])
+if test "$cl_test_CXXFLAGS" != set && test "$ac_compiler_gnu" = yes; then
+    CXXFLAGS="-O"
+fi
+])