diff --git a/os/common/startup/ARMCMx/compilers/GCC/rules.mk b/os/common/startup/ARMCMx/compilers/GCC/rules.mk
index 5026b7c9f..05d782732 100644
--- a/os/common/startup/ARMCMx/compilers/GCC/rules.mk
+++ b/os/common/startup/ARMCMx/compilers/GCC/rules.mk
@@ -127,17 +127,20 @@ ifneq ($(strip $(TSRC)),)
   CFLAGS   += -DTHUMB_PRESENT
   CPPFLAGS += -DTHUMB_PRESENT
   ASFLAGS  += -DTHUMB_PRESENT
+  ASXFLAGS += -DTHUMB_PRESENT
   ifneq ($(strip $(ASRC)),)
     # Mixed ARM and THUMB mode.
     CFLAGS   += -mthumb-interwork
     CPPFLAGS += -mthumb-interwork
     ASFLAGS  += -mthumb-interwork
+    ASXFLAGS += -mthumb-interwork
     LDFLAGS  += -mthumb-interwork
   else
     # Pure THUMB mode, THUMB C code cannot be called by ARM asm code directly.
     CFLAGS   += -mno-thumb-interwork -DTHUMB_NO_INTERWORKING
     CPPFLAGS += -mno-thumb-interwork -DTHUMB_NO_INTERWORKING
     ASFLAGS  += -mno-thumb-interwork -DTHUMB_NO_INTERWORKING -mthumb
+    ASXFLAGS += -mno-thumb-interwork -DTHUMB_NO_INTERWORKING -mthumb
     LDFLAGS  += -mno-thumb-interwork -mthumb
   endif
 else
@@ -145,11 +148,13 @@ else
   CFLAGS   += -mno-thumb-interwork
   CPPFLAGS += -mno-thumb-interwork
   ASFLAGS  += -mno-thumb-interwork
+  ASXFLAGS += -mno-thumb-interwork
   LDFLAGS  += -mno-thumb-interwork
 endif
 
 # Generate dependency information
 ASFLAGS  += -MD -MP -MF .dep/$(@F).d
+ASXFLAGS += -MD -MP -MF .dep/$(@F).d
 CFLAGS   += -MD -MP -MF .dep/$(@F).d
 CPPFLAGS += -MD -MP -MF .dep/$(@F).d
 
diff --git a/readme.txt b/readme.txt
index cd2a3e3b9..ed2570413 100644
--- a/readme.txt
+++ b/readme.txt
@@ -147,6 +147,8 @@
 - RT:  Merged RT4.
 - NIL: Merged NIL2.
 - NIL: Added STM32F7 demo.
+- HAL: Fixed Makefile dependencies not generated for .S files (bug #787)
+       (backported to 16.1.6, 3.0.6).
 - HAL: Fixed OTGv1 driver not functional on STM32L4 (bug #786)(backported
        to 16.1.6).
 - HAL: Fixed wrong bit offset in STM32F37x ADC_CR2_EXTSEL_SRC() macro