diff --git a/m4/nut_check_libavahi.m4 b/m4/nut_check_libavahi.m4
index d49ea063ca..0e8782a366 100644
--- a/m4/nut_check_libavahi.m4
+++ b/m4/nut_check_libavahi.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBAVAHI],
 [
 if test -z "${nut_have_avahi_seen}"; then
 	nut_have_avahi_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libfreeipmi.m4 b/m4/nut_check_libfreeipmi.m4
index 85b4912152..1d563013e1 100644
--- a/m4/nut_check_libfreeipmi.m4
+++ b/m4/nut_check_libfreeipmi.m4
@@ -8,7 +8,7 @@ AC_DEFUN([NUT_CHECK_LIBFREEIPMI],
 [
 if test -z "${nut_have_libfreeipmi_seen}"; then
 	nut_have_libfreeipmi_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libgd.m4 b/m4/nut_check_libgd.m4
index b8d4329710..fbba3a8624 100644
--- a/m4/nut_check_libgd.m4
+++ b/m4/nut_check_libgd.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBGD],
 [
 if test -z "${nut_have_libgd_seen}"; then
 	nut_have_libgd_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	CFLAGS_ORIG="${CFLAGS}"
 	LDFLAGS_ORIG="${LDFLAGS}"
diff --git a/m4/nut_check_libgpiod.m4 b/m4/nut_check_libgpiod.m4
index e5f50cfecb..dd2b0b5cf9 100644
--- a/m4/nut_check_libgpiod.m4
+++ b/m4/nut_check_libgpiod.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBGPIO],
 [
 if test -z "${nut_have_gpio_seen}"; then
 	nut_have_gpio_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libmodbus.m4 b/m4/nut_check_libmodbus.m4
index 359a7ea36c..cf312d4d77 100644
--- a/m4/nut_check_libmodbus.m4
+++ b/m4/nut_check_libmodbus.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBMODBUS],
 [
 if test -z "${nut_have_libmodbus_seen}"; then
 	nut_have_libmodbus_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
@@ -73,29 +73,35 @@ if test -z "${nut_have_libmodbus_seen}"; then
 	CFLAGS="${CFLAGS_ORIG} ${depCFLAGS}"
 	LIBS="${LIBS_ORIG} ${depLIBS}"
 	AC_CHECK_HEADERS(modbus.h, [nut_have_libmodbus=yes], [nut_have_libmodbus=no], [AC_INCLUDES_DEFAULT])
-	AC_CHECK_FUNCS(modbus_new_rtu, [], [nut_have_libmodbus=no])
-	AC_CHECK_FUNCS(modbus_new_tcp, [], [nut_have_libmodbus=no])
-	AC_CHECK_FUNCS(modbus_set_byte_timeout, [], [nut_have_libmodbus=no])
-	AC_CHECK_FUNCS(modbus_set_response_timeout, [], [nut_have_libmodbus=no])
+	AS_IF([test x"${nut_have_libmodbus}" = xyes ], [
+		AC_CHECK_FUNCS(modbus_new_rtu, [], [nut_have_libmodbus=no])
+		AC_CHECK_FUNCS(modbus_new_tcp, [], [nut_have_libmodbus=no])
+		AC_CHECK_FUNCS(modbus_set_byte_timeout, [], [nut_have_libmodbus=no])
+		AC_CHECK_FUNCS(modbus_set_response_timeout, [], [nut_have_libmodbus=no])
+	])
 
-	AC_CHECK_FUNCS(modbus_new_rtu_usb, [nut_have_libmodbus_usb=yes], [
-		nut_have_libmodbus_usb=no
-		AS_IF([test x"${nut_with_usb}" != xno && test x"${nut_with_modbus}" != xno && test x"${nut_have_libmodbus}" = xyes ], [
-			dnl Retry with LibUSB dependency settings if we
-			dnl know we are not opposed to pulling it in.
-			dnl Static libmodbus builds do not refer to
-			dnl (shared) libusb for example.
-			NUT_CHECK_LIBUSB
-			AC_MSG_NOTICE([Retry detection of libmodbus USB support])
-			CFLAGS="$CFLAGS $LIBUSB_CFLAGS"
-			LIBS="$LIBS $LIBUSB_LIBS"
-			unset ac_cv_func_modbus_new_rtu_usb
-			AC_CHECK_FUNCS(modbus_new_rtu_usb, [nut_have_libmodbus_usb=yes], [
-				AS_IF([test x"${nut_with_usb}" = xyes && test x"${nut_with_modbus}" = xyes && test x"${nut_have_libmodbus}" = xyes ], [
-					AC_MSG_WARN([Both --with-modbus and --with-usb were requested, and a libmodbus was found, but it seems to not support USB. You may require a custom build per https://github.com/networkupstools/nut/wiki/APC-UPS-with-Modbus-protocol])
+	AS_IF([test x"${nut_have_libmodbus}" = xyes ], [
+		AC_CHECK_FUNCS(modbus_new_rtu_usb, [nut_have_libmodbus_usb=yes], [
+			nut_have_libmodbus_usb=no
+			AS_IF([test x"${nut_with_usb}" != xno && test x"${nut_with_modbus}" != xno && test x"${nut_have_libmodbus}" = xyes ], [
+				dnl Retry with LibUSB dependency settings if we
+				dnl know we are not opposed to pulling it in.
+				dnl Static libmodbus builds do not refer to
+				dnl (shared) libusb for example.
+				AC_REQUIRE([NUT_CHECK_LIBUSB])
+				AC_MSG_NOTICE([Retry detection of libmodbus USB support])
+				CFLAGS="$CFLAGS $LIBUSB_CFLAGS"
+				LIBS="$LIBS $LIBUSB_LIBS"
+				unset ac_cv_func_modbus_new_rtu_usb
+				AC_CHECK_FUNCS(modbus_new_rtu_usb, [nut_have_libmodbus_usb=yes], [
+					AS_IF([test x"${nut_with_usb}" = xyes && test x"${nut_with_modbus}" = xyes && test x"${nut_have_libmodbus}" = xyes ], [
+						AC_MSG_WARN([Both --with-modbus and --with-usb were requested, and a libmodbus was found, but it seems to not support USB. You may require a custom build per https://github.com/networkupstools/nut/wiki/APC-UPS-with-Modbus-protocol])
+					])
 				])
 			])
 		])
+	], [
+		nut_have_libmodbus_usb=no
 	])
 
 	dnl modbus_set_byte_timeout() and modbus_set_response_timeout()
diff --git a/m4/nut_check_libneon.m4 b/m4/nut_check_libneon.m4
index 864b83b8ef..a20d8328fb 100644
--- a/m4/nut_check_libneon.m4
+++ b/m4/nut_check_libneon.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBNEON],
 [
 if test -z "${nut_have_neon_seen}"; then
 	nut_have_neon_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libnetsnmp.m4 b/m4/nut_check_libnetsnmp.m4
index 9e11e5b29e..78d5fa9d61 100644
--- a/m4/nut_check_libnetsnmp.m4
+++ b/m4/nut_check_libnetsnmp.m4
@@ -8,7 +8,7 @@ AC_DEFUN([NUT_CHECK_LIBNETSNMP],
 [
 if test -z "${nut_have_libnetsnmp_seen}"; then
 	nut_have_libnetsnmp_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 	AC_LANG_PUSH([C])
 
 	dnl save CFLAGS and LIBS
diff --git a/m4/nut_check_libnss.m4 b/m4/nut_check_libnss.m4
index 89ae23d81b..f3b0a60bf1 100644
--- a/m4/nut_check_libnss.m4
+++ b/m4/nut_check_libnss.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBNSS],
 [
 if test -z "${nut_have_libnss_seen}"; then
 	nut_have_libnss_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libopenssl.m4 b/m4/nut_check_libopenssl.m4
index 88c5651bdd..0eeaa13260 100644
--- a/m4/nut_check_libopenssl.m4
+++ b/m4/nut_check_libopenssl.m4
@@ -8,7 +8,7 @@ AC_DEFUN([NUT_CHECK_LIBOPENSSL],
 [
 if test -z "${nut_have_libopenssl_seen}"; then
 	nut_have_libopenssl_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libpowerman.m4 b/m4/nut_check_libpowerman.m4
index 19811632e5..f263a61a31 100644
--- a/m4/nut_check_libpowerman.m4
+++ b/m4/nut_check_libpowerman.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBPOWERMAN],
 [
 if test -z "${nut_have_libpowerman_seen}"; then
 	nut_have_libpowerman_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libregex.m4 b/m4/nut_check_libregex.m4
index 204a6ef560..dd4c49b595 100644
--- a/m4/nut_check_libregex.m4
+++ b/m4/nut_check_libregex.m4
@@ -8,7 +8,7 @@ AC_DEFUN([NUT_CHECK_LIBREGEX],
 [
 if test -z "${nut_have_libregex_seen}"; then
 	nut_have_libregex_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libsystemd.m4 b/m4/nut_check_libsystemd.m4
index 951d6b128d..671c2bb7ce 100644
--- a/m4/nut_check_libsystemd.m4
+++ b/m4/nut_check_libsystemd.m4
@@ -7,7 +7,7 @@ AC_DEFUN([NUT_CHECK_LIBSYSTEMD],
 [
 if test -z "${nut_have_libsystemd_seen}"; then
 	nut_have_libsystemd_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"
diff --git a/m4/nut_check_libusb.m4 b/m4/nut_check_libusb.m4
index 121fd400a3..f85490f51d 100644
--- a/m4/nut_check_libusb.m4
+++ b/m4/nut_check_libusb.m4
@@ -12,10 +12,10 @@ AC_DEFUN([NUT_CHECK_LIBUSB],
 [
 if test -z "${nut_have_libusb_seen}"; then
 	nut_have_libusb_seen=yes
-	NUT_CHECK_PKGCONFIG
+	AC_REQUIRE([NUT_CHECK_PKGCONFIG])
 
 	dnl Our USB matching relies on regex abilities
-	NUT_CHECK_LIBREGEX
+	AC_REQUIRE([NUT_CHECK_LIBREGEX])
 
 	dnl save CFLAGS and LIBS
 	CFLAGS_ORIG="${CFLAGS}"