diff --git a/stmhal/boards/make-pins.py b/stmhal/boards/make-pins.py
index b33c92edc3..371ac77dd8 100755
--- a/stmhal/boards/make-pins.py
+++ b/stmhal/boards/make-pins.py
@@ -14,7 +14,8 @@ SUPPORTED_FN = {
     'I2S'   : ['CK', 'MCK', 'SD', 'WS', 'EXTSD'],
     'USART' : ['RX', 'TX', 'CTS', 'RTS', 'CK'],
     'UART'  : ['RX', 'TX', 'CTS', 'RTS'],
-    'SPI'   : ['NSS', 'SCK', 'MISO', 'MOSI']
+    'SPI'   : ['NSS', 'SCK', 'MISO', 'MOSI'],
+    'SDMMC' : ['CK', 'CMD', 'D0', 'D1', 'D2', 'D3'],
 }
 
 CONDITIONAL_VAR = {
@@ -23,6 +24,7 @@ CONDITIONAL_VAR = {
     'SPI'   : 'MICROPY_HW_SPI{num}_SCK',
     'UART'  : 'MICROPY_HW_UART{num}_TX',
     'USART' : 'MICROPY_HW_UART{num}_TX',
+    'SDMMC' : 'MICROPY_HW_SDMMC{num}_CK',
 }
 
 def parse_port_pin(name_str):
diff --git a/stmhal/pin_defs_stmhal.h b/stmhal/pin_defs_stmhal.h
index 80c967016d..d6a2ef4242 100644
--- a/stmhal/pin_defs_stmhal.h
+++ b/stmhal/pin_defs_stmhal.h
@@ -48,6 +48,7 @@ enum {
   AF_FN_UART = AF_FN_USART,
   AF_FN_SPI,
   AF_FN_I2S,
+  AF_FN_SDMMC,
 };
 
 enum {
@@ -85,6 +86,13 @@ enum {
   AF_PIN_TYPE_I2S_SD,
   AF_PIN_TYPE_I2S_WS,
   AF_PIN_TYPE_I2S_EXTSD,
+
+  AF_PIN_TYPE_SDMMC_CK = 0,
+  AF_PIN_TYPE_SDMMC_CMD,
+  AF_PIN_TYPE_SDMMC_D0,
+  AF_PIN_TYPE_SDMMC_D1,
+  AF_PIN_TYPE_SDMMC_D2,
+  AF_PIN_TYPE_SDMMC_D3,
 };
 
 // The HAL uses a slightly different naming than we chose, so we provide
@@ -109,13 +117,15 @@ enum {
 
 // Note that SPI and I2S are really the same peripheral as far as the HAL
 // is concerned, so there is no I2S_TypeDef.
+// We use void* for SDMMC because not all MCUs have the SDMMC_TypeDef type.
 #define PIN_DEFS_PORT_AF_UNION \
     TIM_TypeDef   *TIM; \
     I2C_TypeDef   *I2C; \
     USART_TypeDef *USART; \
     USART_TypeDef *UART; \
     SPI_TypeDef   *SPI;\
-    SPI_TypeDef   *I2S;
+    SPI_TypeDef   *I2S; \
+    void          *SDMMC; \
 
 typedef GPIO_TypeDef pin_gpio_t;