diff --git a/arch/sim/src/sim/sim_internal.h b/arch/sim/src/sim/sim_internal.h
index 47b0084a22..cb5cccdb14 100644
--- a/arch/sim/src/sim/sim_internal.h
+++ b/arch/sim/src/sim/sim_internal.h
@@ -134,6 +134,12 @@
 
 #ifndef __ASSEMBLY__
 
+/****************************************************************************
+ * Type Declarations
+ ****************************************************************************/
+
+typedef int pid_t;
+
 /****************************************************************************
  * Public Type Definitions
  ****************************************************************************/