Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -20,11 +20,14 @@
 CPP="$OBJCPP"
 CPPFLAGS="$CPPFLAGS $OBJCPPFLAGS"
 OBJCFLAGS="$OBJCFLAGS -Wall -fexceptions -fobjc-exceptions"
 OBJCFLAGS="$OBJCFLAGS -fconstant-string-class=OFConstantString"
 
-AX_CHECK_COMPILER_FLAGS(-std=gnu99, [OBJCFLAGS="$OBJCFLAGS -std=gnu99"])
+AX_CHECK_COMPILER_FLAGS(-std=gnu99, [
+	OBJCFLAGS="$OBJCFLAGS -std=gnu99"
+	AC_SUBST(GNU99, "-std=gnu99")
+])
 AX_CHECK_COMPILER_FLAGS(-fgnu89-inline, [OBJCFLAGS="$OBJCFLAGS -fgnu89-inline"])
 AX_CHECK_COMPILER_FLAGS(-pipe, [OBJCFLAGS="$OBJCFLAGS -pipe"])
 AX_CHECK_COMPILER_FLAGS(-fno-common, [OBJCFLAGS="$OBJCFLAGS -fno-common"])
 AX_CHECK_COMPILER_FLAGS(-fno-constant-cfstrings, [
 	OBJCFLAGS="$OBJCFLAGS -fno-constant-cfstrings"

Index: utils/objfw-config.in
==================================================================
--- utils/objfw-config.in
+++ utils/objfw-config.in
@@ -20,11 +20,11 @@
 libdir="@libdir@"
 CFLAGS=""
 CPPFLAGS="-I@includedir@"
 CXXFLAGS=""
 OBJC="@OBJC@"
-OBJCFLAGS="@GNU_RUNTIME@ -fexceptions -fobjc-exceptions"
+OBJCFLAGS="@GNU99@ @GNU_RUNTIME@ -fexceptions -fobjc-exceptions"
 OBJCFLAGS="$OBJCFLAGS -fconstant-string-class=OFConstantString"
 OBJCFLAGS="$OBJCFLAGS @NO_CONST_CFSTRINGS@ @BLOCKS_FLAGS@ @NO_WARN_UNUSED@"
 LIB_CFLAGS="@LIB_CFLAGS@"
 LIB_LDFLAGS="@LIB_LDFLAGS@"
 LIB_PREFIX="@LIB_PREFIX@"