diff --git a/os/rt/include/ch.h b/os/rt/include/ch.h
index a8cc7ac81..bd8fe92d3 100644
--- a/os/rt/include/ch.h
+++ b/os/rt/include/ch.h
@@ -62,6 +62,10 @@
 #define CH_KERNEL_PATCH         0
 /** @} */
 
+/* Required forward declaration, knowledge of this type is required by all
+   modules.*/
+typedef struct thread thread_t;
+
 /* Core headers.*/
 #include "chtypes.h"
 #include "chconf.h"
diff --git a/os/rt/ports/ARMCMx/chcore_v6m.h b/os/rt/ports/ARMCMx/chcore_v6m.h
index fa6476084..ed05fe6b7 100644
--- a/os/rt/ports/ARMCMx/chcore_v6m.h
+++ b/os/rt/ports/ARMCMx/chcore_v6m.h
@@ -254,7 +254,7 @@ struct port_intctx {
   struct port_intctx *r13 = (struct port_intctx *)__get_PSP();              \
   if ((stkalign_t *)(r13 - 1) < (otp)->p_stklimit)                          \
     chSysHalt("stack overflow");                                            \
-  _port_switch((void *)ntp, (void *)otp);                                   \
+  _port_switch(ntp, otp);                                                   \
 }
 #endif
 
@@ -266,7 +266,7 @@ struct port_intctx {
 extern "C" {
 #endif
   void _port_irq_epilogue(regarm_t lr);
-  void _port_switch(void *ntp, void *otp);
+  void _port_switch(thread_t *ntp, thread_t *otp);
   void _port_thread_start(void);
   void _port_switch_from_isr(void);
   void _port_exit_from_isr(void);
diff --git a/os/rt/ports/ARMCMx/chcore_v7m.h b/os/rt/ports/ARMCMx/chcore_v7m.h
index 9e0b1e9cd..404e87411 100644
--- a/os/rt/ports/ARMCMx/chcore_v7m.h
+++ b/os/rt/ports/ARMCMx/chcore_v7m.h
@@ -344,7 +344,7 @@ struct port_intctx {
   struct port_intctx *r13 = (struct port_intctx *)__get_PSP();              \
   if ((stkalign_t *)(r13 - 1) < (otp)->p_stklimit)                          \
     chSysHalt("stack overflow");                                            \
-  _port_switch((void *)ntp, (void *)otp);                                   \
+  _port_switch(ntp, otp);                                                   \
 }
 #endif
 
@@ -356,7 +356,7 @@ struct port_intctx {
 extern "C" {
 #endif
   void _port_irq_epilogue(void);
-  void _port_switch(void *ntp, void *otp);
+  void _port_switch(thread_t *ntp, thread_t *otp);
   void _port_thread_start(void);
   void _port_switch_from_isr(void);
   void _port_exit_from_isr(void);
diff --git a/os/rt/ports/e200/chcore.h b/os/rt/ports/e200/chcore.h
index a043bb0b0..0255a0f1d 100644
--- a/os/rt/ports/e200/chcore.h
+++ b/os/rt/ports/e200/chcore.h
@@ -340,7 +340,7 @@ struct context {
   register struct port_intctx *sp asm ("%r1");                              \
   if ((stkalign_t *)(sp - 1) < otp->p_stklimit)                             \
     chDbgPanic("stack overflow");                                           \
-  _port_switch((void *)ntp, (void *)otp);                                   \
+  _port_switch(ntp, otp);                                                   \
 }
 #endif
 
@@ -373,7 +373,7 @@ struct context {
 #ifdef __cplusplus
 extern "C" {
 #endif
-  void _port_switch(void *ntp, void *otp);
+  void _port_switch(thread_t *ntp, thread_t *otp);
   void _port_thread_start(void);
 #ifdef __cplusplus
 }