diff --git a/py/circuitpy_mpconfig.h b/py/circuitpy_mpconfig.h
index d0a65a6a7a4aa..4d7510eb7ede0 100644
--- a/py/circuitpy_mpconfig.h
+++ b/py/circuitpy_mpconfig.h
@@ -188,7 +188,9 @@ typedef long mp_off_t;
 
 // Turning off FULL_BUILD removes some functionality to reduce flash size on tiny SAMD21s
 #define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (CIRCUITPY_FULL_BUILD)
+#ifndef MICROPY_CPYTHON_COMPAT
 #define MICROPY_CPYTHON_COMPAT                (CIRCUITPY_FULL_BUILD)
+#endif
 #define MICROPY_PY_BUILTINS_POW3              (CIRCUITPY_BUILTINS_POW3)
 #define MICROPY_COMP_FSTRING_LITERAL          (MICROPY_CPYTHON_COMPAT)
 #define MICROPY_MODULE_WEAK_LINKS             (0)
diff --git a/py/circuitpy_mpconfig.mk b/py/circuitpy_mpconfig.mk
index b486497692779..0e82b31495c11 100644
--- a/py/circuitpy_mpconfig.mk
+++ b/py/circuitpy_mpconfig.mk
@@ -36,6 +36,11 @@ CFLAGS += -DCIRCUITPY_FULL_BUILD=$(CIRCUITPY_FULL_BUILD)
 MICROPY_PY_ASYNC_AWAIT ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DMICROPY_PY_ASYNC_AWAIT=$(MICROPY_PY_ASYNC_AWAIT)
 
+# Non-full builds may optionally set MICROPY_CPYTHON_COMPAT for a few rarely
+# used CPython features. Omitting it reduces flash usage by ~2 KB
+MICROPY_CPYTHON_COMPAT ?= $(CIRCUITPY_FULL_BUILD)
+CFLAGS += -DMICROPY_CPYTHON_COMPAT=$(MICROPY_CPYTHON_COMPAT)
+
 CIRCUITPY_AESIO ?= 0
 CFLAGS += -DCIRCUITPY_AESIO=$(CIRCUITPY_AESIO)