diff --git a/Makefile b/Makefile
index 7e520a1..b5a7295 100644
--- a/Makefile
+++ b/Makefile
@@ -46,7 +46,7 @@ $(TOPDIR)/src/gmp: | $(EVERYTHING_DOWNLOADED)
 	$(MV) gmp-5.0.3 $(TOPDIR)/src/gmp
 
 $(TOPDIR)/src/gmp/Makefile: | $(TOPDIR)/src/gmp
-	(cd src/gmp && ABI="$(GMP_ABI)" CFLAGS="$(CFLAGS)" \
+	(cd src/gmp && ABI="$(ABI)" CFLAGS="$(CFLAGS)" \
    ./configure --disable-shared --enable-static )
 
 $(TOPDIR)/src/gmp/.libs/libgmp.a: $(TOPDIR)/src/gmp/Makefile
diff --git a/configure.ac b/configure.ac
index 764a994..9a4918f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -206,11 +206,15 @@ GCC_FLAG_CHECK(-fno-builtin,gp_cv_gcc_has_no_builtin,
 AC_LANG_POP(C)
 
 dnl Build with GMP?
-int_library=integer-simple
 AC_ARG_ENABLE([gmp],
   [AC_HELP_STRING([--enable-gmp],
                   [Build with gmp instead of integer-simple])],
-  [int_library=integer-gmp])
+  [if test "$enableval" = "yes"; then
+     int_library=integer-gmp
+   else
+     int_library=integer-simple
+   fi],
+  [int_library=integer-simple])
 AC_SUBST(INTEGER_LIBRARY, [$int_library])
 
 dnl -------------------------------------------------------------------------