diff --git a/LUFA/Build/lufa.atprogram.in b/LUFA/Build/lufa.atprogram.in
index 95b0a9702f0f1a33fb153e796ec12d939205054e..f9f5dfc9c88f01b2e6de129530db697e695ec83a 100644
--- a/LUFA/Build/lufa.atprogram.in
+++ b/LUFA/Build/lufa.atprogram.in
@@ -48,9 +48,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Default values of optionally user-supplied variables
 ATPROGRAM_PROGRAMMER ?= jtagice3
diff --git a/LUFA/Build/lufa.avrdude.in b/LUFA/Build/lufa.avrdude.in
index 595e4957486efad15277477d2851433075e798ce..21f93ef26aaf9356b787f9d720cae0b75b27ecb8 100644
--- a/LUFA/Build/lufa.avrdude.in
+++ b/LUFA/Build/lufa.avrdude.in
@@ -48,9 +48,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Default values of optionally user-supplied variables
 AVRDUDE_PROGRAMMER ?= jtagicemkii
diff --git a/LUFA/Build/lufa.build.in b/LUFA/Build/lufa.build.in
index 7eb65878dda6712a6700f7e1bc3f832e746225d8..994f4b7fde084d412fc3ead461db4687e66b8804 100644
--- a/LUFA/Build/lufa.build.in
+++ b/LUFA/Build/lufa.build.in
@@ -68,9 +68,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Default values of optionally user-supplied variables
 BOARD           ?= NONE
diff --git a/LUFA/Build/lufa.core.in b/LUFA/Build/lufa.core.in
index 96b6df36650f5822423b961a02080a4bbb60c2b4..f44b407edb85e33f62edfa330e270d210507d841 100644
--- a/LUFA/Build/lufa.core.in
+++ b/LUFA/Build/lufa.core.in
@@ -51,6 +51,8 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
+SHELL = /bin/sh
+
 # Build sorted and filtered lists of the included build module data
 SORTED_LUFA_BUILD_MODULES   = $(sort $(LUFA_BUILD_MODULES))
 SORTED_LUFA_BUILD_TARGETS   = $(sort $(LUFA_BUILD_TARGETS))
diff --git a/LUFA/Build/lufa.cppcheck.in b/LUFA/Build/lufa.cppcheck.in
index 66f3aeef560d523a5b386433db6a87d935b2356b..1593a42791aece0ca6f9a9c3030712e8cde03387 100644
--- a/LUFA/Build/lufa.cppcheck.in
+++ b/LUFA/Build/lufa.cppcheck.in
@@ -54,9 +54,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Default values of optionally user-supplied variables
 CPPCHECK_INCLUDES            ?=
diff --git a/LUFA/Build/lufa.dfu.in b/LUFA/Build/lufa.dfu.in
index 7eb1fa08e2303ff1bb237b4c8521f72c3d25bd41..ba75f14a7926b81dca3f1eb5fed88c3ed3a0794d 100644
--- a/LUFA/Build/lufa.dfu.in
+++ b/LUFA/Build/lufa.dfu.in
@@ -46,9 +46,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Sanity-check values of mandatory user-supplied variables
 $(foreach MANDATORY_VAR, $(LUFA_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))
diff --git a/LUFA/Build/lufa.doxygen.in b/LUFA/Build/lufa.doxygen.in
index 2d8c28db32679968fb3bd2dc99df44976be28155..baca62f604f3f88ba5910fb8a4b48509f96682c4 100644
--- a/LUFA/Build/lufa.doxygen.in
+++ b/LUFA/Build/lufa.doxygen.in
@@ -45,9 +45,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Default values of optionally user-supplied variables
 DOXYGEN_CONF            ?= Doxygen.conf
diff --git a/LUFA/Build/lufa.sources.in b/LUFA/Build/lufa.sources.in
index d5316ba87c0f0d94c141ac1d4ce48095434dda46..a475ece09a9c1cc03d67644efda1e138c0edfc82 100644
--- a/LUFA/Build/lufa.sources.in
+++ b/LUFA/Build/lufa.sources.in
@@ -52,9 +52,11 @@ LUFA_BUILD_PROVIDED_MACROS +=
 #
 # -----------------------------------------------------------------------------
 
-ERROR_IF_UNSET   = $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
-ERROR_IF_EMPTY   = $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
-ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
+SHELL = /bin/sh
+
+ERROR_IF_UNSET   ?= $(if $(filter undefined, $(origin $(strip $(1)))), $(error Makefile $(strip $(1)) value not set))
+ERROR_IF_EMPTY   ?= $(if $(strip $($(strip $(1)))), , $(error Makefile $(strip $(1)) option cannot be blank))
+ERROR_IF_NONBOOL ?= $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(strip $(1)) option must be Y or N))
 
 # Sanity check user supplied values
 $(foreach MANDATORY_VAR, $(LUFA_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))