diff --git a/closed/GensrcJ9JCL.gmk b/closed/GensrcJ9JCL.gmk
index 8b9b1b75ef3..4cfe82477da 100644
--- a/closed/GensrcJ9JCL.gmk
+++ b/closed/GensrcJ9JCL.gmk
@@ -61,7 +61,7 @@ $(J9JCL_SOURCES_DONEFILE) : \
 	@$(MKDIR) -p $(J9TOOLS_DIR)
 	$(MAKE) $(MAKE_ARGS) -C $(OPENJ9_TOPDIR)/sourcetools -f buildj9tools.mk \
 		BOOT_JDK=$(BOOT_JDK) \
-		DEST_DIR=$(call FixPath,$(J9TOOLS_DIR)) \
+		DEST_DIR=$(call MixedPath,$(J9TOOLS_DIR)) \
 		JAVA_HOME=$(BOOT_JDK) \
 		preprocessor
 	@$(ECHO) Generating J9JCL sources
diff --git a/closed/JPP.gmk b/closed/JPP.gmk
index cc95d6261fd..a9474f2916f 100644
--- a/closed/JPP.gmk
+++ b/closed/JPP.gmk
@@ -36,28 +36,17 @@ endif # OPENJ9_ENABLE_INLINE_TYPES
 # $3 - destination subdirectory
 # $4 - more options (optional)
 define RunJPP
-	@$(ECHO) $(BOOT_JDK)/bin/java \
-		-cp "$(call FixPath,$(JPP_JAR))" \
+	$(call EchoAndRun, $(BOOT_JDK)/bin/java \
+		-cp "$(call MixedPath,$(JPP_JAR))" \
 		-Dfile.encoding=US-ASCII \
 		com.ibm.jpp.commandline.CommandlineBuilder \
 			-verdict \
 			-config $1 \
-			-baseDir "$(call FixPath,$(dir $2))" \
+			-baseDir "$(call MixedPath,$(dir $2))" \
 			-srcRoot $(notdir $2)/ \
-			-xml "$(call FixPath,$(OPENJ9_TOPDIR)/jcl/jpp_configuration.xml)" \
-			-dest "$(call FixPath,$(SUPPORT_OUTPUTDIR)$(strip $3))" \
+			-xml "$(call MixedPath,$(OPENJ9_TOPDIR)/jcl/jpp_configuration.xml)" \
+			-dest "$(call MixedPath,$(SUPPORT_OUTPUTDIR)$(strip $3))" \
 			-tag:define "$(subst $(SPACE),;,$(sort $(JPP_TAGS)))" \
-			$4
-	@$(BOOT_JDK)/bin/java \
-		-cp "$(call FixPath,$(JPP_JAR))" \
-		-Dfile.encoding=US-ASCII \
-		com.ibm.jpp.commandline.CommandlineBuilder \
-			-verdict \
-			-config $1 \
-			-baseDir "$(call FixPath,$(dir $2))" \
-			-srcRoot $(notdir $2)/ \
-			-xml "$(call FixPath,$(OPENJ9_TOPDIR)/jcl/jpp_configuration.xml)" \
-			-dest "$(call FixPath,$(SUPPORT_OUTPUTDIR)$(strip $3))" \
-			-tag:define "$(subst $(SPACE),;,$(sort $(JPP_TAGS)))" \
-			$4
+			$4 \
+		)
 endef # RunJPP
diff --git a/closed/OpenJ9.gmk b/closed/OpenJ9.gmk
index 7de6de33042..83d937eb37b 100644
--- a/closed/OpenJ9.gmk
+++ b/closed/OpenJ9.gmk
@@ -27,6 +27,7 @@ ifeq (,$(wildcard $(SPEC)))
 endif
 include $(SPEC)
 include $(TOPDIR)/make/common/MakeBase.gmk
+include $(TOPDIR)/closed/JPP.gmk
 
 ifeq (,$(BUILD_ID))
   BUILD_ID := 000000
@@ -318,8 +319,6 @@ $(foreach file, \
 	$(notdir $(wildcard $(OPENJ9_TOPDIR)/buildspecs/*)), \
 	$(eval $(call openj9_stage_buildspec_file,$(file))))
 
-J9TOOLS_DIR := $(SUPPORT_OUTPUTDIR)/j9tools
-
 stage-j9 :
 	@$(ECHO) Staging OpenJ9 runtime in $(OUTPUTDIR)/vm
 	$(call openj9_copy_tree,$(OUTPUTDIR)/vm,$(OPENJ9_TOPDIR)/runtime)
@@ -484,13 +483,13 @@ run-preprocessors-j9 : stage-j9
 	+BOOT_JDK=$(BOOT_JDK) $(EXPORT_COMPILER_ENV_VARS) OPENJDK_VERSION_NUMBER_FOUR_POSITIONS=$(VERSION_NUMBER_FOUR_POSITIONS) \
 		$(MAKE) $(MAKE_ARGS) -C $(OUTPUTDIR)/vm -f $(OPENJ9_TOPDIR)/runtime/buildtools.mk \
 			BUILD_ID=$(BUILD_ID) \
-			DEST_DIR=$(call FixPath,$(J9TOOLS_DIR)) \
+			DEST_DIR=$(call MixedPath,$(J9TOOLS_DIR)) \
 			EXTRA_CONFIGURE_ARGS=$(OMR_EXTRA_CONFIGURE_ARGS) \
 			FREEMARKER_JAR="$(FREEMARKER_JAR)" \
 			J9VM_SHA=$(OPENJ9_SHA) \
 			JAVA_HOME=$(BOOT_JDK) \
 			OMR_DIR=$(OUTPUTDIR)/vm/omr \
-			SOURCETOOLS_DIR=$(call FixPath,$(OPENJ9_TOPDIR))/sourcetools \
+			SOURCETOOLS_DIR=$(call MixedPath,$(OPENJ9_TOPDIR))/sourcetools \
 			SPEC=$(OPENJ9_BUILDSPEC) \
 			UMA_OPTIONS_EXTRA="-buildDate $(shell date +'%Y%m%d')" \
 			VERSION_MAJOR=$(VERSION_FEATURE) \
diff --git a/closed/custom/common/MakeBase.gmk b/closed/custom/common/MakeBase.gmk
new file mode 100644
index 00000000000..bc55724eefe
--- /dev/null
+++ b/closed/custom/common/MakeBase.gmk
@@ -0,0 +1,34 @@
+# ===========================================================================
+# (c) Copyright IBM Corp. 2023, 2023 All Rights Reserved
+# ===========================================================================
+# This code is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License version 2 only, as
+# published by the Free Software Foundation.
+#
+# IBM designates this particular file as subject to the "Classpath" exception
+# as provided by IBM in the LICENSE file that accompanied this code.
+#
+# This code is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+# version 2 for more details (a copy is included in the LICENSE file that
+# accompanied this code).
+#
+# You should have received a copy of the GNU General Public License version
+# 2 along with this work; if not, see <http://www.gnu.org/licenses/>.
+# ===========================================================================
+
+# Echo a command and then execute it.
+# $1 - the command
+define EchoAndRun
+	@ $(ECHO) $1
+	@ $1
+endef
+
+# On Windows, FixPath yields backslashes which can cause problems, so
+# we use PATHTOOL instead for tools (like java) that support both.
+ifeq ($(call isTargetOs, windows), true)
+  MixedPath = $(shell $(PATHTOOL) -m $1)
+else
+  MixedPath = $1
+endif