diff --git a/Makefile.in b/Makefile.in
index 7c8c6e0..ddf9060 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,9 +1,9 @@
 
 CC= @CC@
-CSTD= -std=c99 -Wall -D_POSIX_C_SOURCE=200112L
+CSTD= @CSTD@ -Wall -D_POSIX_C_SOURCE=200112L
 CFLAGS= $(CSTD) @CFLAGS@ -DED25519_@ED25519IMPL@ @MYDEFS@
 ASFLAGS=
-LDFLAGS= -no-pie
+LDFLAGS= @NOPIE@
 MV= mv
 
 ED25519_DEFS= -DED25519_ref10 -DED25519_amd64_51_30k -DED25519_amd64_64_24k -DED25519_donna
diff --git a/configure.ac b/configure.ac
index 9f2cb3e..04786be 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2,9 +2,51 @@ AC_INIT(mkp224o)
 # sanity check
 AC_CONFIG_SRCDIR([main.c])
 # C compiler
-: ${CFLAGS="-O3 -march=native -fomit-frame-pointer"}
+oldcflags="$CFLAGS"
 AC_PROG_CC
 
+if test "x$oldcflags" != "x$CFLAGS"
+then
+	oldcflags="-O3"
+	CFLAGS="-march=native"
+	AC_MSG_CHECKING([whether CC supports -march=native])
+	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+		[AC_MSG_RESULT([yes])]
+		[oldcflags="$oldcflags -march=native"],
+		[AC_MSG_RESULT([no])]
+	)
+	CFLAGS="-fomit-frame-pointer"
+	AC_MSG_CHECKING([whether CC supports -fomit-frame-pointer])
+	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+		[AC_MSG_RESULT([yes])]
+		[oldcflags="$oldcflags -fomit-frame-pointer"],
+		[AC_MSG_RESULT([no])]
+	)
+	CFLAGS="$oldcflags"
+fi
+
+cstd=""
+oldcflags="$CFLAGS"
+CFLAGS="-std=c99"
+AC_MSG_CHECKING([whether CC supports -std=c99])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+    [AC_MSG_RESULT([yes])]
+    [cstd="-std=c99"],
+    [AC_MSG_RESULT([no])]
+)
+CFLAGS="$oldcflags"
+
+nopie=""
+oldcflags="$CFLAGS"
+CFLAGS="-no-pie"
+AC_MSG_CHECKING([whether CC supports -no-pie])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+    [AC_MSG_RESULT([yes])]
+    [nopie="-no-pie"],
+    [AC_MSG_RESULT([no])]
+)
+CFLAGS="$oldcflags"
+
 MYDEFS=""
 
 ed25519impl=""
@@ -92,6 +134,8 @@ then
 	MYDEFS="$MYDEFS -DSTATISTICS"
 fi
 
+AC_SUBST(CSTD,["$cstd"])
 AC_SUBST(ED25519IMPL,["$ed25519impl"])
 AC_SUBST(MYDEFS,["$MYDEFS"])
+AC_SUBST(NOPIE,["$nopie"])
 AC_OUTPUT(Makefile)