diff --git a/core/vb.c b/core/vb.c
index b37f2c1..67c18de 100644
--- a/core/vb.c
+++ b/core/vb.c
@@ -900,7 +900,7 @@ VBAPI vbOnWrite vbSetWriteCallback(VB *sim, vbOnWrite callback) {
 }
 
 /* Determine the size of a simulation instance */
-VBAPI size_t vbSizeOf() {
+VBAPI size_t vbSizeOf(void) {
     return sizeof (VB);
 }
 
diff --git a/core/vb.h b/core/vb.h
index 803862c..023dda8 100644
--- a/core/vb.h
+++ b/core/vb.h
@@ -166,7 +166,7 @@ VBAPI vbOnSamples   vbSetSamplesCallback  (VB *sim, vbOnSamples callback);
 VBAPI uint32_t      vbSetSystemRegister   (VB *sim, unsigned index, uint32_t value);
 VBAPI void*         vbSetUserData         (VB *sim, void *tag);
 VBAPI vbOnWrite     vbSetWriteCallback    (VB *sim, vbOnWrite callback);
-VBAPI size_t        vbSizeOf              ();
+VBAPI size_t        vbSizeOf              (void);
 VBAPI int32_t       vbWrite               (VB *sim, uint32_t address, int type, int32_t value);