diff --git a/ports/broadcom/mpconfigport.mk b/ports/broadcom/mpconfigport.mk
index f29f48d545..c7b8a2fcc3 100644
--- a/ports/broadcom/mpconfigport.mk
+++ b/ports/broadcom/mpconfigport.mk
@@ -1,3 +1,22 @@
+# Define an equivalent for MICROPY_LONGINT_IMPL, to pass to $(MPY-TOOL) in py/mkrules.mk
+# $(MPY-TOOL) needs to know what kind of longint to use (if any) to freeze long integers.
+# This should correspond to the MICROPY_LONGINT_IMPL definition in mpconfigport.h.
+
+ifeq ($(LONGINT_IMPL),NONE)
+MPY_TOOL_LONGINT_IMPL = -mlongint-impl=none
+endif
+
+ifeq ($(LONGINT_IMPL),MPZ)
+MPY_TOOL_LONGINT_IMPL = -mlongint-impl=mpz
+endif
+
+ifeq ($(LONGINT_IMPL),LONGLONG)
+MPY_TOOL_LONGINT_IMPL = -mlongint-impl=longlong
+endif
+
+# All broadcom ports have longints.
+LONGINT_IMPL = MPZ
+
 # Typically the first module to create
 CIRCUITPY_MICROCONTROLLER = 1
 # Typically the second module to create