diff --git a/ports/esp32/Makefile b/ports/esp32/Makefile
index 239618c6f7..9d57ee4c21 100644
--- a/ports/esp32/Makefile
+++ b/ports/esp32/Makefile
@@ -17,8 +17,13 @@ ifeq ($(wildcard $(BOARD_DIR)/.),)
 $(error Invalid BOARD specified: $(BOARD_DIR))
 endif
 
-# If the build directory is not given, make it reflect the board name.
+# If the build directory is not given, make it reflect the board name (and
+# optionally the board variant).
+ifneq ($(BOARD_VARIANT),)
+BUILD ?= build-$(BOARD)-$(BOARD_VARIANT)
+else
 BUILD ?= build-$(BOARD)
+endif
 
 # Device serial settings.
 PORT ?= /dev/ttyUSB0
diff --git a/ports/rp2/Makefile b/ports/rp2/Makefile
index ccfc1ac7d6..fdca11d11e 100644
--- a/ports/rp2/Makefile
+++ b/ports/rp2/Makefile
@@ -16,8 +16,14 @@ endif
 ifeq ($(wildcard $(BOARD_DIR)/.),)
 $(error Invalid BOARD specified: $(BOARD_DIR))
 endif
- 
+
+# If the build directory is not given, make it reflect the board name (and
+# optionally the board variant).
+ifneq ($(BOARD_VARIANT),)
+BUILD ?= build-$(BOARD)-$(BOARD_VARIANT)
+else
 BUILD ?= build-$(BOARD)
+endif
 
 $(VERBOSE)MAKESILENT = -s
 
diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index 7051398970..475d8f1004 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -13,8 +13,13 @@ ifeq ($(wildcard $(BOARD_DIR)/.),)
 $(error Invalid BOARD specified: $(BOARD_DIR))
 endif
 
-# If the build directory is not given, make it reflect the board name.
+# If the build directory is not given, make it reflect the board name (and
+# optionally the board variant).
+ifneq ($(BOARD_VARIANT),)
+BUILD ?= build-$(BOARD)-$(BOARD_VARIANT)
+else
 BUILD ?= build-$(BOARD)
+endif
 
 include ../../py/mkenv.mk
 -include mpconfigport.mk