diff --git a/sourcehook/sourcehook.cpp b/sourcehook/sourcehook.cpp
index d9f6731..2f4aa30 100644
--- a/sourcehook/sourcehook.cpp
+++ b/sourcehook/sourcehook.cpp
@@ -96,7 +96,7 @@ namespace SourceHook
 				{
 					if (p1->paramsPassInfo[i].type != p2->paramsPassInfo[i].type)
 						return false;
-					if (p1->paramsPassInfo[i].flags != p2->paramsPassInfo[i].flags)
+					if (GetRealFlags(p1->paramsPassInfo[i]) != GetRealFlags(p2->paramsPassInfo[i]))
 						return false;
 				}
 			}
diff --git a/sourcehook/sourcehook_impl_cproto.h b/sourcehook/sourcehook_impl_cproto.h
index a3b32d7..347ffd4 100644
--- a/sourcehook/sourcehook_impl_cproto.h
+++ b/sourcehook/sourcehook_impl_cproto.h
@@ -70,9 +70,15 @@ namespace SourceHook
 				return m_Proto;
 			}
 
+			// For old sourcehook.h: flags 0 -> assume ByVal
+			static unsigned int GetRealFlags(const PassInfo &info)
+			{
+				return (info.flags == 0) ? PassInfo::PassFlag_ByVal : info.flags;
+			}
+
 			static size_t GetRealSize(const PassInfo &info)
 			{
-				if (info.flags & PassInfo::PassFlag_ByRef)
+				if (GetRealFlags(info) & PassInfo::PassFlag_ByRef)
 				{
 					return sizeof(void*);
 				}