diff --git a/ChangeLog b/ChangeLog
index ce44209db..5cae22383 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2011-07-03  Robert Larice
+ * configure.ac :
+   enable -Wconversion
+     remove -Wimplicit-function-declaration since its implicit in -Wall
+     Note: -Wuninitialized is implicit in -Wall but may not be effective for -O0
+
 2011-07-03  Robert Larice
  * src/Makefile.am ,
  * src/makeidx.c :
diff --git a/configure.ac b/configure.ac
index bce2a6454..b3f28d188 100644
--- a/configure.ac
+++ b/configure.ac
@@ -203,7 +203,7 @@ dnl the above AC_PROG_CC may set CFLAGS to "-O2 -g"
 if test "$enable_debug" = "no"; then
 	if test "x$GCC" = "xyes"; then
 		AC_MSG_WARN(Removing debugging option!)
-		CFLAGS="$ext_CFLAGS -O2 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wimplicit-function-declaration -Wnested-externs -Wold-style-definition -Wredundant-decls -s"
+		CFLAGS="$ext_CFLAGS -O2 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wnested-externs -Wold-style-definition -Wredundant-decls -Wconversion -s"
 	else
 		AC_MSG_WARN(Removing debugging option!)
 		CFLAGS="$ext_CFLAGS -O2"
@@ -211,7 +211,7 @@ if test "$enable_debug" = "no"; then
 else
     AC_DEFINE(NGDEBUG,1,[Compile with debug info])
 	if test "x$GCC" = "xyes"; then
-		CFLAGS="$ext_CFLAGS -g -O0 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wimplicit-function-declaration -Wnested-externs -Wold-style-definition -Wredundant-decls"
+		CFLAGS="$ext_CFLAGS -g -O0 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wnested-externs -Wold-style-definition -Wredundant-decls -Wconversion"
 	else
 		CFLAGS="$ext_CFLAGS -g"
 	fi