diff --git a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
index 59f1551111..742d5f2458 100644
--- a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
+++ b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
@@ -965,7 +965,8 @@ void dcd_edpt_close (uint8_t rhport, uint8_t ep_addr)
   (void)rhport;
 
   xfer_ctl_t * xfer = xfer_ctl_ptr(ep_addr);
-  uint8_t const epnum = xfer->epnum;
+  // Fix -Werror=null-dereference
+  uint8_t const epnum = ((xfer_ctl_t *)xfer)->epnum;
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
   if(dir == TUSB_DIR_IN)
@@ -1004,7 +1005,6 @@ bool dcd_edpt_iso_activate(uint8_t rhport,  tusb_desc_endpoint_t const * p_endpo
 {
   (void)rhport;
   uint8_t const epnum = xfer_ctl_ptr(p_endpoint_desc->bEndpointAddress)->epnum;
-  uint8_t const dir   = tu_edpt_dir(p_endpoint_desc->bEndpointAddress);
   const uint16_t packet_size = tu_edpt_packet_size(p_endpoint_desc);
   uint16_t pma_addr;
 
@@ -1071,7 +1071,8 @@ bool dcd_edpt_xfer (uint8_t rhport, uint8_t ep_addr, uint8_t * buffer, uint16_t
   (void) rhport;
 
   xfer_ctl_t * xfer = xfer_ctl_ptr(ep_addr);
-  uint8_t const epnum = xfer->epnum;
+  // Fix -Werror=null-dereference
+  uint8_t const epnum = ((xfer_ctl_t *)xfer)->epnum;
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
   xfer->buffer = buffer;
@@ -1108,7 +1109,8 @@ bool dcd_edpt_xfer_fifo (uint8_t rhport, uint8_t ep_addr, tu_fifo_t * ff, uint16
   (void) rhport;
 
   xfer_ctl_t * xfer = xfer_ctl_ptr(ep_addr);
-  uint8_t const epnum = xfer->epnum;
+  // Fix -Werror=null-dereference
+  uint8_t const epnum = ((xfer_ctl_t *)xfer)->epnum;
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
   xfer->buffer = NULL;
@@ -1138,7 +1140,8 @@ void dcd_edpt_stall (uint8_t rhport, uint8_t ep_addr)
   (void)rhport;
 
   xfer_ctl_t * xfer = xfer_ctl_ptr(ep_addr);
-  uint8_t const epnum = xfer->epnum;
+  // Fix -Werror=null-dereference
+  uint8_t const epnum = ((xfer_ctl_t *)xfer)->epnum;
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
   if (dir == TUSB_DIR_IN)
@@ -1156,7 +1159,8 @@ void dcd_edpt_clear_stall (uint8_t rhport, uint8_t ep_addr)
   (void)rhport;
 
   xfer_ctl_t * xfer = xfer_ctl_ptr(ep_addr);
-  uint8_t const epnum = xfer->epnum;
+  // Fix -Werror=null-dereference
+  uint8_t const epnum = ((xfer_ctl_t *)xfer)->epnum;
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
   if (dir == TUSB_DIR_IN)
diff --git a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev_pvt_st.h b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev_pvt_st.h
index b64776fc95..3823746146 100644
--- a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev_pvt_st.h
+++ b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev_pvt_st.h
@@ -234,7 +234,7 @@ TU_ATTR_ALWAYS_INLINE static inline void pcd_set_ep_cnt_reg(__O uint16_t * pdwRe
   /* There should be no remainder in the above calculation */
   TU_ASSERT((wCount - (numblocks * (blocksize ? 32 : 2))) == 0, /**/);
 
-  /* Encode into register. When BLSIZE==1, we need to substract 1 block count */
+  /* Encode into register. When BLSIZE==1, we need to subtract 1 block count */
   *pdwReg = (blocksize << 15) | ((numblocks - blocksize) << 10);
 }