diff --git a/py/circuitpy_defns.mk b/py/circuitpy_defns.mk
index 5c5f05ca3a..5fc6b1fa16 100644
--- a/py/circuitpy_defns.mk
+++ b/py/circuitpy_defns.mk
@@ -390,9 +390,6 @@ SRC_COMMON_HAL_ALL = \
 	alarm/time/TimeAlarm.c \
 	alarm/touch/TouchAlarm.c \
 	analogio/AnalogIn.c \
-#ifdef CIRCUITPYTHON_ANALOGFASTIN
-	analogio/AnalogFastIn.c \
-#endif
 	analogio/AnalogOut.c \
 	analogio/__init__.c \
 	audiobusio/I2SOut.c \
@@ -482,6 +479,13 @@ SRC_C += \
 
 endif
 
+ifeq ($(CIRCUITPYTHON_ANALOGFASTIN),1)
+# Needed for AnalogFastIn
+SRC_COMMON_HAL_ALL += \
+	analogio/AnalogFastIn.c \
+
+endif
+
 
 SRC_COMMON_HAL = $(filter $(SRC_PATTERNS), $(SRC_COMMON_HAL_ALL))