diff --git a/config_host.mk.in b/config_host.mk.in
index 1d5a83add0c0..c1cd96717707 100644
--- a/config_host.mk.in
+++ b/config_host.mk.in
@@ -789,3 +789,7 @@ include $(BUILDDIR)/config_$(gb_Side)_lang.mk
 # tarball names
 # does use some of the variables defined above
 include @SRC_ROOT@/download.lst
+
+# prep for WSL-as-helper-builds where build runs from within git-bash/MSYS that would otherwise
+# messes with anything that looks like a path (starts with /) but it cannot resolve
+export MSYS_NO_PATHCONV=1
\ No newline at end of file
diff --git a/external/beanshell/ExternalProject_beanshell.mk b/external/beanshell/ExternalProject_beanshell.mk
index 450ac2b706dd..604b3571fe44 100644
--- a/external/beanshell/ExternalProject_beanshell.mk
+++ b/external/beanshell/ExternalProject_beanshell.mk
@@ -16,7 +16,7 @@ $(eval $(call gb_ExternalProject_register_targets,beanshell,\
 $(call gb_ExternalProject_get_state_target,beanshell,build) :
 	$(call gb_Trace_StartRange,beanshell,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-	JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+	unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 	$(ICECREAM_RUN) "$(ANT)" \
 		$(if $(verbose),-v,-q) \
 		-f build.xml \
diff --git a/external/hsqldb/ExternalProject_hsqldb.mk b/external/hsqldb/ExternalProject_hsqldb.mk
index 67ae75106bc2..4e5c750c7f3c 100644
--- a/external/hsqldb/ExternalProject_hsqldb.mk
+++ b/external/hsqldb/ExternalProject_hsqldb.mk
@@ -21,7 +21,7 @@ $(eval $(call gb_ExternalProject_register_targets,hsqldb,\
 $(call gb_ExternalProject_get_state_target,hsqldb,build) :
 	$(call gb_Trace_StartRange,hsqldb,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(if $(JDK_SECURITYMANAGER_DISALLOWED_FOR_BUILD), \
 		    ANT_OPTS="$$ANT_OPTS -Djava.security.manager=allow") \
 		$(ICECREAM_RUN) "$(ANT)" \
diff --git a/external/java_websocket/ExternalProject_java_websocket.mk b/external/java_websocket/ExternalProject_java_websocket.mk
index 0d713aadc02d..9d4a62d81183 100644
--- a/external/java_websocket/ExternalProject_java_websocket.mk
+++ b/external/java_websocket/ExternalProject_java_websocket.mk
@@ -16,7 +16,7 @@ $(eval $(call gb_ExternalProject_register_targets,java_websocket,\
 $(call gb_ExternalProject_get_state_target,java_websocket,build) :
 	$(call gb_Trace_StartRange,java_websocket,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_flow_engine.mk b/external/jfreereport/ExternalProject_jfreereport_flow_engine.mk
index 55868ea9bac9..a41206b506f0 100644
--- a/external/jfreereport/ExternalProject_jfreereport_flow_engine.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_flow_engine.mk
@@ -20,7 +20,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_flow_engine,\
 $(call gb_ExternalProject_get_state_target,jfreereport_flow_engine,build) :
 	$(call gb_Trace_StartRange,jfreereport_flow_engine,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_flute.mk b/external/jfreereport/ExternalProject_jfreereport_flute.mk
index 120c98cbdbb4..1a57167246c0 100644
--- a/external/jfreereport/ExternalProject_jfreereport_flute.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_flute.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_flute,\
 $(call gb_ExternalProject_get_state_target,jfreereport_flute,build) :
 	$(call gb_Trace_StartRange,jfreereport_flute,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_libbase.mk b/external/jfreereport/ExternalProject_jfreereport_libbase.mk
index 6d97ffa5762a..864b13ed1519 100644
--- a/external/jfreereport/ExternalProject_jfreereport_libbase.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_libbase.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_libbase,\
 $(call gb_ExternalProject_get_state_target,jfreereport_libbase,build) :
 	$(call gb_Trace_StartRange,jfreereport_libbase,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_libfonts.mk b/external/jfreereport/ExternalProject_jfreereport_libfonts.mk
index 9a6edf0b891f..6b7da7b5c52b 100644
--- a/external/jfreereport/ExternalProject_jfreereport_libfonts.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_libfonts.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_libfonts,\
 $(call gb_ExternalProject_get_state_target,jfreereport_libfonts,build) :
 	$(call gb_Trace_StartRange,jfreereport_libfonts,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_libformula.mk b/external/jfreereport/ExternalProject_jfreereport_libformula.mk
index 1182873e66aa..5211d54fbca9 100644
--- a/external/jfreereport/ExternalProject_jfreereport_libformula.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_libformula.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_libformula,\
 $(call gb_ExternalProject_get_state_target,jfreereport_libformula,build) :
 	$(call gb_Trace_StartRange,jfreereport_libformula,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_liblayout.mk b/external/jfreereport/ExternalProject_jfreereport_liblayout.mk
index 7c7478e07368..0ea331570b77 100644
--- a/external/jfreereport/ExternalProject_jfreereport_liblayout.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_liblayout.mk
@@ -28,7 +28,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_liblayout,\
 $(call gb_ExternalProject_get_state_target,jfreereport_liblayout,build) :
 	$(call gb_Trace_StartRange,jfreereport_liblayout,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_libloader.mk b/external/jfreereport/ExternalProject_jfreereport_libloader.mk
index ddb34e3d8614..5c5964b9e17a 100644
--- a/external/jfreereport/ExternalProject_jfreereport_libloader.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_libloader.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_libloader,\
 $(call gb_ExternalProject_get_state_target,jfreereport_libloader,build) :
 	$(call gb_Trace_StartRange,jfreereport_libloader,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_librepository.mk b/external/jfreereport/ExternalProject_jfreereport_librepository.mk
index 59fa203fbe63..49d7e9497fb9 100644
--- a/external/jfreereport/ExternalProject_jfreereport_librepository.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_librepository.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_librepository,\
 $(call gb_ExternalProject_get_state_target,jfreereport_librepository,build) :
 	$(call gb_Trace_StartRange,jfreereport_librepository,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_libserializer.mk b/external/jfreereport/ExternalProject_jfreereport_libserializer.mk
index 1226e14206d4..d0d37a59bded 100644
--- a/external/jfreereport/ExternalProject_jfreereport_libserializer.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_libserializer.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_libserializer,\
 $(call gb_ExternalProject_get_state_target,jfreereport_libserializer,build) :
 	$(call gb_Trace_StartRange,jfreereport_libserializer,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_libxml.mk b/external/jfreereport/ExternalProject_jfreereport_libxml.mk
index 295573ec67ab..f79bf3731eac 100644
--- a/external/jfreereport/ExternalProject_jfreereport_libxml.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_libxml.mk
@@ -19,7 +19,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_libxml,\
 $(call gb_ExternalProject_get_state_target,jfreereport_libxml,build) :
 	$(call gb_Trace_StartRange,jfreereport_libxml,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/jfreereport/ExternalProject_jfreereport_sac.mk b/external/jfreereport/ExternalProject_jfreereport_sac.mk
index a33186183ee7..807f30e37ab5 100644
--- a/external/jfreereport/ExternalProject_jfreereport_sac.mk
+++ b/external/jfreereport/ExternalProject_jfreereport_sac.mk
@@ -16,7 +16,7 @@ $(eval $(call gb_ExternalProject_register_targets,jfreereport_sac,\
 $(call gb_ExternalProject_get_state_target,jfreereport_sac,build) :
 	$(call gb_Trace_StartRange,jfreereport_sac,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
+		unset MSYS_NO_PATHCONV && JAVA_HOME=$(JAVA_HOME_FOR_BUILD) \
 		$(ICECREAM_RUN) "$(ANT)" \
 			$(if $(verbose),-v,-q) \
 			-f build.xml \
diff --git a/external/libcdr/ExternalProject_libcdr.mk b/external/libcdr/ExternalProject_libcdr.mk
index c9f5401ac43f..3a4be9d9ce73 100644
--- a/external/libcdr/ExternalProject_libcdr.mk
+++ b/external/libcdr/ExternalProject_libcdr.mk
@@ -27,7 +27,7 @@ $(call gb_ExternalProject_get_state_target,libcdr,build) :
 	$(call gb_Trace_StartRange,libcdr,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \
diff --git a/external/libebook/ExternalProject_libebook.mk b/external/libebook/ExternalProject_libebook.mk
index 9760be7d298b..e1b04df38087 100644
--- a/external/libebook/ExternalProject_libebook.mk
+++ b/external/libebook/ExternalProject_libebook.mk
@@ -28,7 +28,7 @@ $(call gb_ExternalProject_get_state_target,libebook,build) :
 	$(call gb_Trace_StartRange,libebook,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \
diff --git a/external/libepubgen/ExternalProject_libepubgen.mk b/external/libepubgen/ExternalProject_libepubgen.mk
index f0dbf70a2eb2..0f34d10665e4 100644
--- a/external/libepubgen/ExternalProject_libepubgen.mk
+++ b/external/libepubgen/ExternalProject_libepubgen.mk
@@ -24,7 +24,7 @@ $(call gb_ExternalProject_get_state_target,libepubgen,build) :
 	$(call gb_Trace_StartRange,libepubgen,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \
diff --git a/external/libfreehand/ExternalProject_libfreehand.mk b/external/libfreehand/ExternalProject_libfreehand.mk
index 554017cafd5f..a3b4859bb3af 100644
--- a/external/libfreehand/ExternalProject_libfreehand.mk
+++ b/external/libfreehand/ExternalProject_libfreehand.mk
@@ -27,7 +27,7 @@ $(call gb_ExternalProject_get_state_target,libfreehand,build) :
 	$(call gb_Trace_StartRange,libfreehand,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \
diff --git a/external/liblangtag/ExternalProject_liblangtag.mk b/external/liblangtag/ExternalProject_liblangtag.mk
index a682250ebe8e..4e07b9fe4278 100644
--- a/external/liblangtag/ExternalProject_liblangtag.mk
+++ b/external/liblangtag/ExternalProject_liblangtag.mk
@@ -20,7 +20,7 @@ $(eval $(call gb_ExternalProject_register_targets,liblangtag,\
 $(call gb_ExternalProject_get_state_target,liblangtag,build):
 	$(call gb_Trace_StartRange,liblangtag,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
-		MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure --disable-modules --disable-test --disable-introspection --with-pic \
+		unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure --disable-modules --disable-test --disable-introspection --with-pic \
 		$(if $(or $(DISABLE_DYNLOADING),$(filter MSC,$(COM))), \
 			--disable-shared --enable-static, \
 			--enable-shared --disable-static) \
diff --git a/external/libqxp/ExternalProject_libqxp.mk b/external/libqxp/ExternalProject_libqxp.mk
index fea48ffc4b11..0cafe24e0634 100644
--- a/external/libqxp/ExternalProject_libqxp.mk
+++ b/external/libqxp/ExternalProject_libqxp.mk
@@ -25,7 +25,7 @@ $(call gb_ExternalProject_get_state_target,libqxp,build) :
 	$(call gb_Trace_StartRange,libqxp,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \
diff --git a/external/libvisio/ExternalProject_libvisio.mk b/external/libvisio/ExternalProject_libvisio.mk
index 01fe27290f45..abf7cbd728df 100644
--- a/external/libvisio/ExternalProject_libvisio.mk
+++ b/external/libvisio/ExternalProject_libvisio.mk
@@ -26,7 +26,7 @@ $(call gb_ExternalProject_get_state_target,libvisio,build) :
 	$(call gb_Trace_StartRange,libvisio,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \
diff --git a/external/libzmf/ExternalProject_libzmf.mk b/external/libzmf/ExternalProject_libzmf.mk
index 1a338526c12b..2bba4d2e427a 100644
--- a/external/libzmf/ExternalProject_libzmf.mk
+++ b/external/libzmf/ExternalProject_libzmf.mk
@@ -27,7 +27,7 @@ $(call gb_ExternalProject_get_state_target,libzmf,build) :
 	$(call gb_Trace_StartRange,libzmf,EXTERNAL)
 	$(call gb_ExternalProject_run,build,\
 		export PKG_CONFIG="" \
-		&& MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
+		&& unset MSYS_NO_PATHCONV && MAKE=$(MAKE) $(gb_RUN_CONFIGURE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \