diff --git a/src/pkcs11/pkcs11-spy.c b/src/pkcs11/pkcs11-spy.c
index df71e483..07b02fd9 100644
--- a/src/pkcs11/pkcs11-spy.c
+++ b/src/pkcs11/pkcs11-spy.c
@@ -1469,6 +1469,9 @@ C_WaitForSlotEvent(CK_FLAGS flags, CK_SLOT_ID_PTR pSlot, CK_VOID_PTR pRserved)
 
 	enter("C_WaitForSlotEvent");
 	spy_dump_ulong_in("flags", flags);
+	if (pSlot != NULL) {
+		spy_dump_ulong_in("pSlot", *pSlot);
+	}
 	rv = po->C_WaitForSlotEvent(flags, pSlot, pRserved);
 	return retne(rv);
 }