diff --git a/src/truetype/ttinterp.c b/src/truetype/ttinterp.c
index 3b7b21cca..0ac0f9e12 100644
--- a/src/truetype/ttinterp.c
+++ b/src/truetype/ttinterp.c
@@ -7670,8 +7670,10 @@
   /* documentation is in ttinterp.h */
 
   FT_EXPORT_DEF( FT_Error )
-  TT_RunIns( TT_ExecContext  exc )
+  TT_RunIns( void*  exec )
   {
+    TT_ExecContext  exc = (TT_ExecContext)exec;
+
     FT_ULong   ins_counter = 0;  /* executed instructions counter */
     FT_ULong   num_twilight_points;
     FT_UShort  i;
diff --git a/src/truetype/ttinterp.h b/src/truetype/ttinterp.h
index 891e2123c..48d493af8 100644
--- a/src/truetype/ttinterp.h
+++ b/src/truetype/ttinterp.h
@@ -528,7 +528,7 @@ FT_BEGIN_HEADER
    *   invoked by the TrueType debugger.
    */
   FT_EXPORT( FT_Error )
-  TT_RunIns( TT_ExecContext  exec );
+  TT_RunIns( void*  exec );
 
 
 FT_END_HEADER