--- a/ports/unix/Makefile
+++ b/ports/unix/Makefile
@@ -31,7 +31,7 @@
 QSTR_GLOBAL_DEPENDENCIES += $(VARIANT_DIR)/mpconfigvariant.h
 
 # OS name, for simple autoconfig
-UNAME_S := $(shell uname -s)
+UNAME_S := @UNAME_S@
 
 # include py core make definitions
 include $(TOP)/py/py.mk
@@ -151,7 +151,7 @@
 # If the variant enables it, enable modbluetooth.
 ifeq ($(MICROPY_PY_BLUETOOTH),1)
 ifeq ($(MICROPY_BLUETOOTH_BTSTACK),1)
-HAVE_LIBUSB := $(shell (which pkg-config > /dev/null && pkg-config --exists libusb-1.0) 2>/dev/null && echo '1')
+HAVE_LIBUSB := $(shell (which @PKG_CONFIG@ > /dev/null && @PKG_CONFIG@ --exists libusb-1.0) 2>/dev/null && echo '1')
 
 # Figure out which BTstack transport to use.
 ifeq ($(HAVE_LIBUSB),1)
@@ -180,8 +180,8 @@
  endif
 else
 # Use system version of libffi.
-LIBFFI_CFLAGS := $(shell pkg-config --cflags libffi)
-LIBFFI_LDFLAGS := $(shell pkg-config --libs libffi)
+LIBFFI_CFLAGS := $(shell @PKG_CONFIG@ --cflags libffi)
+LIBFFI_LDFLAGS := $(shell @PKG_CONFIG@ --libs libffi)
 endif
 
 ifeq ($(UNAME_S),Linux)