diff --git a/.gitignore b/.gitignore
index d1cb67fa..010439ab 100644
--- a/.gitignore
+++ b/.gitignore
@@ -27,6 +27,7 @@
 /libtool
 /stamp-h1
 # In-tree build, only top-level
+/apisupport-config.h
 /cpusupport-config.h
 # In-tree build, all directories
 .dirstamp
diff --git a/Makefile.am b/Makefile.am
index e6b9fe1a..a3f265ed 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -93,6 +93,7 @@ AM_CPPFLAGS=		-I$(srcdir)/lib				\
 			-I$(srcdir)/libcperciva/crypto		\
 			-I$(srcdir)/libcperciva/util		\
 			-DCPUSUPPORT_CONFIG_FILE=\"cpusupport-config.h\" \
+			-DAPISUPPORT_CONFIG_FILE=\"apisupport-config.h\" \
 			-D_POSIX_C_SOURCE=200809L		\
 			-D_XOPEN_SOURCE=700			\
 			${CFLAGS_POSIX}
@@ -105,10 +106,15 @@ scrypt_LDADD=		libcperciva_aesni.la libcperciva_rdrand.la \
 			${LDADD_POSIX}
 scrypt_man_MANS=	scrypt.1
 
+# apisupport needs to access post-configure info: lib-platform/platform.h,
+# config.h, and -DHAVE_CONFIG_H.
+apisupport-config.h:
+	( export CC="${CC}"; export CFLAGS="-I${top_srcdir}/lib-platform -I${builddir} ${DEFS} ${CFLAGS}"; command -p sh $(srcdir)/libcperciva/apisupport/Build/apisupport.sh "$$PATH") > apisupport-config.h.tmp && command -p mv apisupport-config.h.tmp apisupport-config.h
 cpusupport-config.h:
 	( export CC="${CC}"; export CFLAGS="${CFLAGS}"; command -p sh $(srcdir)/libcperciva/cpusupport/Build/cpusupport.sh "$$PATH") > cpusupport-config.h.tmp && command -p mv cpusupport-config.h.tmp cpusupport-config.h
-BUILT_SOURCES=	cpusupport-config.h
-CLEANFILES=	cpusupport-config.h cpusupport-config.h.tmp
+BUILT_SOURCES=	apisupport-config.h cpusupport-config.h
+CLEANFILES=	apisupport-config.h apisupport-config.h.tmp	\
+		cpusupport-config.h cpusupport-config.h.tmp
 
 # Libraries from libcperciva code.
 noinst_LTLIBRARIES=	libcperciva_aesni.la
@@ -151,7 +157,7 @@ libscrypt_sse2_la_CFLAGS=`. ./cpusupport-config.h; echo $${CFLAGS_X86_SSE2}`
 noinst_LTLIBRARIES+=	libscrypt_memlimit.la
 libscrypt_memlimit_la_SOURCES=	lib-platform/util/memlimit.c	\
 				lib-platform/util/memlimit.h
-libscrypt_memlimit_la_CFLAGS=-U_POSIX_C_SOURCE -U_XOPEN_SOURCE
+libscrypt_memlimit_la_CFLAGS=`. ./apisupport-config.h; echo $${CFLAGS_NONPOSIX_MEMLIMIT}`
 
 # Install libscrypt-kdf?
 if LIBSCRYPT_KDF
diff --git a/libcperciva/apisupport/Build/apisupport-NONPOSIX-MEMLIMIT.c b/libcperciva/apisupport/Build/apisupport-NONPOSIX-MEMLIMIT.c
new file mode 100644
index 00000000..d585ab21
--- /dev/null
+++ b/libcperciva/apisupport/Build/apisupport-NONPOSIX-MEMLIMIT.c
@@ -0,0 +1,19 @@
+#include "platform.h"
+
+#ifdef HAVE_SYS_PARAM_H
+#include <sys/param.h>
+#endif
+#ifdef HAVE_SYS_SYSCTL_H
+#include <sys/sysctl.h>
+#endif
+#ifdef HAVE_SYS_SYSINFO_H
+#include <sys/sysinfo.h>
+#endif
+
+int
+main(void)
+{
+
+	/* Success! */
+	return (0);
+}
diff --git a/libcperciva/apisupport/Build/apisupport.sh b/libcperciva/apisupport/Build/apisupport.sh
new file mode 100755
index 00000000..aedd5662
--- /dev/null
+++ b/libcperciva/apisupport/Build/apisupport.sh
@@ -0,0 +1,85 @@
+# Should be sourced by `command -p sh path/to/apisupport.sh "$PATH"` from
+# within a Makefile.
+if ! [ "${PATH}" = "$1" ]; then
+	echo "WARNING: POSIX violation: ${SHELL}'s command -p resets \$PATH" 1>&2
+	PATH=$1
+fi
+
+# Standard output should be written to apisupport-config.h, which is both a
+# C header file defining APISUPPORT_PLATFORM_FEATURE macros and sourceable sh
+# code which sets CFLAGS_PLATFORM_FEATURE environment variables.
+SRCDIR=$(command -p dirname "$0")
+
+CFLAGS_HARDCODED="-D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700"
+
+# Do we want to record stderr to a file?
+if [ "${DEBUG:-0}" -eq "0" ]; then
+	outcc="/dev/null"
+else
+	outcc="apisupport-stderr.log"
+	rm -f "${outcc}"
+fi
+
+feature() {
+	PLATFORM=$1
+	FEATURE=$2
+	EXTRALIB=$3
+	shift 3;
+
+	# Bail if we didn't include this feature in this source tree.
+	feature_filename="${SRCDIR}/apisupport-${PLATFORM}-${FEATURE}.c"
+	if ! [ -f "${feature_filename}" ]; then
+		return
+	fi
+
+	# Check if we can compile this feature (and any required arguments).
+	printf "Checking if compiler supports %s %s feature..."		\
+	    "${PLATFORM}" "${FEATURE}" 1>&2
+	for API_CFLAGS in "$@"; do
+		if ${CC} ${CPPFLAGS} ${CFLAGS} ${CFLAGS_HARDCODED}	\
+		    ${API_CFLAGS} "${feature_filename}" ${LDADD_EXTRA}	\
+		    ${EXTRALIB}	2>>"${outcc}"; then
+			rm -f a.out
+			break;
+		fi
+		API_CFLAGS=NOTSUPPORTED;
+	done
+	case ${API_CFLAGS} in
+	NOTSUPPORTED)
+		echo " no" 1>&2
+		;;
+	"")
+		echo " yes" 1>&2
+		echo "#define APISUPPORT_${PLATFORM}_${FEATURE} 1"
+		;;
+	*)
+		echo " yes, via ${API_CFLAGS}" 1>&2
+		echo "#define APISUPPORT_${PLATFORM}_${FEATURE} 1"
+		echo "#ifdef apisupport_dummy"
+		echo "export CFLAGS_${PLATFORM}_${FEATURE}=\"${API_CFLAGS}\""
+		echo "#endif"
+		;;
+	esac
+}
+
+if [ "$2" = "--all" ]; then
+	feature() {
+		PLATFORM=$1
+		FEATURE=$2
+		echo "#define APISUPPORT_${PLATFORM}_${FEATURE} 1"
+	}
+fi
+
+# Detect how to compile non-POSIX code.
+feature NONPOSIX SETGROUPS "" ""			\
+	"-U_POSIX_C_SOURCE -U_XOPEN_SOURCE"		\
+	"-U_POSIX_C_SOURCE -U_XOPEN_SOURCE -Wno-reserved-id-macro"
+feature NONPOSIX MEMLIMIT "" ""				\
+	"-U_POSIX_C_SOURCE -U_XOPEN_SOURCE"		\
+	"-U_POSIX_C_SOURCE -U_XOPEN_SOURCE -Wno-reserved-id-macro"
+
+# Detect how to compile libssl and libcrypto code.
+feature LIBSSL HOST_NAME "-lssl" ""			\
+	"-Wno-cast-qual"
+feature LIBCRYPTO LOW_LEVEL_AES "-lcrypto" ""		\
+	"-Wno-deprecated-declarations"