diff --git a/NEWS.adoc b/NEWS.adoc
index 6d88f0fd75..047e4801c3 100644
--- a/NEWS.adoc
+++ b/NEWS.adoc
@@ -286,6 +286,9 @@ https://github.com/networkupstools/nut/milestone/12
      to bumping the debug verbosity of `upsdrvctl` tool. [#3276]
    * If we fail to stop a driver by signal (e.g. PID file was not saved),
      retry to `INSTCMD driver.exit` it by socket protocol. [#3277]
+   * The NUT Integration Testing suite now also involves `upsdrvctl` to
+     run one driver instance indirectly, helping make check-NIT` catch
+     portability issues with different builds of the tool. [#2800, #3292]
 
  - `upslog` tool updates:
    * Updated `help()` and failure messages to suggest `-m '*,-'` for logging
diff --git a/configure.ac b/configure.ac
index e7bc787c86..ddee6dd565 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6708,10 +6708,13 @@ AS_CASE([${target_os}],
         AC_MSG_NOTICE([FWIW, assuming ABS_TOP_SRCDIR="$ABS_TOP_SRCDIR" and ABS_TOP_BUILDDIR="$ABS_TOP_BUILDDIR"])
 ])
 
-dnl Use these at best for tests (e.g. nutconf), not production code:
+dnl Use these at best for tests (e.g. nutconf, NIT), not production code:
 AC_DEFINE_UNQUOTED([ABS_TOP_SRCDIR], ["${ABS_TOP_SRCDIR}"], [NUT source directory when the build was configured])
 AC_DEFINE_UNQUOTED([ABS_TOP_BUILDDIR], ["${ABS_TOP_BUILDDIR}"], [NUT build directory when the build was configured])
 
+AC_SUBST(ABS_TOP_SRCDIR)
+AC_SUBST(ABS_TOP_BUILDDIR)
+
 dnl ---------------------------------------------------------------------
 AC_MSG_CHECKING([whether to install External API integration script: Enphase Monitor])
 nut_with_extapi_enphase="no"
diff --git a/drivers/upsdrvctl.c b/drivers/upsdrvctl.c
index a6ba76b459..475d4a6d49 100644
--- a/drivers/upsdrvctl.c
+++ b/drivers/upsdrvctl.c
@@ -943,7 +943,7 @@ static void forkexec(char *const argv[], const ups_t *ups)
 	BOOL	ret;
 	DWORD	res;
 	DWORD	exit_code = 0;
-	char	commandline[SMALLBUF];
+	char	commandline[LARGEBUF];
 	STARTUPINFO	StartupInfo;
 	PROCESS_INFORMATION	ProcessInformation;
 	int	i = 1;
@@ -951,15 +951,30 @@ static void forkexec(char *const argv[], const ups_t *ups)
 	memset(&StartupInfo, 0, sizeof(STARTUPINFO));
 
 	/* the command line is made of the driver name followed by args */
-	snprintf(commandline, sizeof(commandline), "%s", ups->driver);
+	if (strstr(argv[0], ups->driver)) {
+		/* We already know whom to call (got a pointer to needle in the haystack) */
+		snprintf(commandline, sizeof(commandline), "%s", argv[0]);
+	} else {
+		/* Hope for the PATH based resolution to work, perhaps the
+		 * driver program is located nearby (depends on configure
+		 * options). Note that for builds tested in the workspace
+		 * this may be misleading ("nearby" is under ".libs/" and
+		 * fails to run directly without the tweaks of libtool
+		 * wrapper provided in the directory just above).
+		 */
+		snprintf(commandline, sizeof(commandline), "%s%s", ups->driver, EXEEXT);
+	}
+
 	while (argv[i] != NULL) {
 		snprintfcat(commandline, sizeof(commandline), " %s", argv[i]);
 		i++;
 	}
 
+	upsdebugx(1, "%s[WIN32]: CreateProcess(argv0='%s' cmdline='%s')...",
+		__func__, argv[0], commandline);
 	ret = CreateProcess(
-			argv[0],
-			commandline,
+			argv[0],	/* Application/Module name, often the program to run */
+			commandline,	/* Full command line including the program to run and its args */
 			NULL,
 			NULL,
 			FALSE,
@@ -1237,7 +1252,10 @@ static void start_driver(const ups_t *ups)
 #ifndef WIN32
 	snprintf(dfn, sizeof(dfn), "%s/%s", driverpath, ups->driver);
 #else	/* WIN32 */
-	snprintf(dfn, sizeof(dfn), "%s/%s.exe", driverpath, ups->driver);
+	if (driverpath && *driverpath == '/')
+		snprintf(dfn, sizeof(dfn), "%s/%s.exe", driverpath, ups->driver);
+	else	/* Assume windows-style path with backslashes */
+		snprintf(dfn, sizeof(dfn), "%s\\%s.exe", driverpath, ups->driver);
 #endif	/* WIN32 */
 	ret = stat(dfn, &fs);
 
diff --git a/tests/NIT/Makefile.am b/tests/NIT/Makefile.am
index 8332bac658..0d1aea3f2c 100644
--- a/tests/NIT/Makefile.am
+++ b/tests/NIT/Makefile.am
@@ -13,10 +13,16 @@ EXTRA_DIST = nit.sh README.adoc
 
 if WITH_CHECK_NIT
 check: check-NIT
-else
+else !WITH_CHECK_NIT
 check:
 	@echo "NO-OP: $@ in `pwd` is inactive by default. Run 'configure --enable-check-NIT' or 'make check-NIT' explicitly" >&2
-endif
+endif !WITH_CHECK_NIT
+
+# Paths possibly different from what automake provides (POSIXish)
+# when building on/for e.g. Windows. Matters where system() is used,
+# such as NIT suite using/testing upsdrvctl:
+ABS_TOP_SRCDIR = @ABS_TOP_SRCDIR@
+ABS_TOP_BUILDDIR = @ABS_TOP_BUILDDIR@
 
 # Run in builddir, use script from srcdir
 # Avoid running "$<" - not all make implementations handle that
@@ -25,6 +31,7 @@ check-NIT: $(abs_srcdir)/nit.sh
 	BUILTIN_RUN_AS_USER='$(RUN_AS_USER)' BUILTIN_RUN_AS_GROUP='$(RUN_AS_GROUP)' \
 	abs_srcdir='$(abs_srcdir)' abs_builddir='$(abs_builddir)' \
 	abs_top_srcdir='$(abs_top_srcdir)' abs_top_builddir='$(abs_top_builddir)' \
+	ABS_TOP_SRCDIR='$(ABS_TOP_SRCDIR)' ABS_TOP_BUILDDIR='$(ABS_TOP_BUILDDIR)' \
 	EXEEXT='$(EXEEXT)' \
 	"$(abs_srcdir)/nit.sh"
 
@@ -48,6 +55,7 @@ check-NIT-sandbox: $(abs_srcdir)/nit.sh
 	BUILTIN_RUN_AS_USER='$(RUN_AS_USER)' BUILTIN_RUN_AS_GROUP='$(RUN_AS_GROUP)' \
 	abs_srcdir='$(abs_srcdir)' abs_builddir='$(abs_builddir)' \
 	abs_top_srcdir='$(abs_top_srcdir)' abs_top_builddir='$(abs_top_builddir)' \
+	ABS_TOP_SRCDIR='$(ABS_TOP_SRCDIR)' ABS_TOP_BUILDDIR='$(ABS_TOP_BUILDDIR)' \
 	EXEEXT='$(EXEEXT)' \
 	"$(abs_srcdir)/nit.sh"
 
diff --git a/tests/NIT/nit.sh b/tests/NIT/nit.sh
index 0db5378c85..43df6e47fc 100755
--- a/tests/NIT/nit.sh
+++ b/tests/NIT/nit.sh
@@ -53,7 +53,7 @@
 #   different value like "nobody" or "nogroup" would be defaulted for test.
 #
 # Copyright
-#	2022-2025 Jim Klimov <jimklimov+nut@gmail.com>
+#	2022-2026 Jim Klimov <jimklimov+nut@gmail.com>
 #
 # License: GPLv2+
 
@@ -427,7 +427,7 @@ else
 fi
 
 log_info "Locating NUT programs to test:"
-for PROG in upsd upsc dummy-ups upsmon upslog upssched ; do
+for PROG in upsd upsc dummy-ups upsdrvctl upsmon upslog upssched ; do
     (command -v ${PROG}) || (command -v ${PROG}${EXEEXT-}) || die "Useless setup: ${PROG} not found in PATH: ${PATH}"
 done
 
@@ -1000,9 +1000,24 @@ generatecfg_upsmon_secondary() {
 generatecfg_ups_trivial() {
     # Populate the configs for the run
     (   echo 'maxretry = 3' > "$NUT_CONFPATH/ups.conf" || exit
-        if [ x"${TOP_BUILDDIR}" != x ]; then
-            echo "driverpath = \"${TOP_BUILDDIR}/drivers\"" >> "$NUT_CONFPATH/ups.conf" || exit
+        if [ x"${ABS_TOP_BUILDDIR}" != x ]; then
+            # NOTE: Windows backslashes are pre-escaped in the configure-generated value
+            case "${ABS_TOP_BUILDDIR}" in
+                ?":\\"*) PATHSEP='\\' ;;
+                *) PATHSEP="/" ;;
+            esac
+            echo "driverpath = \"${ABS_TOP_BUILDDIR}${PATHSEP}drivers\"" >> "$NUT_CONFPATH/ups.conf" || exit
+        else
+            # NOTE: Escaping presumed needed below, so for PATHSEP too
+            if [ x"${TOP_BUILDDIR}" != x ]; then
+                case "${TOP_BUILDDIR}" in
+                    ?":\\"*) PATHSEP='\' ;;
+                    *) PATHSEP="/" ;;
+                esac
+                echo "driverpath = \"${TOP_BUILDDIR}${PATHSEP}drivers\"" | sed 's,\\,\\\\,g' >> "$NUT_CONFPATH/ups.conf" || exit
+            fi
         fi
+        unset PATHSEP
         if [ -n "${NUT_DEBUG_MIN-}" ] ; then
             echo "debug_min = ${NUT_DEBUG_MIN}" >> "$NUT_CONFPATH/ups.conf" || exit
         fi
@@ -1359,8 +1374,9 @@ sandbox_start_drivers() {
     if [ -n "${NUT_DEBUG_LEVEL_DRIVERS-}" ]; then
         NUT_DEBUG_LEVEL="${NUT_DEBUG_LEVEL_DRIVERS}"
     fi
-    #execcmd upsdrvctl ${ARG_FG} ${ARG_USER} start dummy &
-    execcmd dummy-ups -a dummy ${ARG_USER} ${ARG_FG} &
+    # Run one driver instance indirectly, to test the upsdrvctl tool too:
+    execcmd upsdrvctl ${ARG_FG} ${ARG_USER} start dummy &
+    #execcmd dummy-ups -a dummy ${ARG_USER} ${ARG_FG} &
     PID_DUMMYUPS="$!"
     log_debug "Tried to start dummy-ups driver for 'dummy' as PID $PID_DUMMYUPS"