diff --git a/LEGO1/legostream.cpp b/LEGO1/legostream.cpp
index 7f2e5387..1fd2bf11 100644
--- a/LEGO1/legostream.cpp
+++ b/LEGO1/legostream.cpp
@@ -4,6 +4,13 @@
 #include <cstdio>
 #include <string>
 
+// Very likely but not certain sizes.
+// The classes are only used on the stack in functions we have not 100% matched
+// yet, we can confirm the size once we have.
+DECOMP_SIZE_ASSERT(LegoStream, 0x8);
+DECOMP_SIZE_ASSERT(LegoFileStream, 0xC);
+DECOMP_SIZE_ASSERT(LegoMemoryStream, 0x10);
+
 // OFFSET: LEGO1 0x10045ae0
 MxBool LegoStream::IsWriteMode()
 {
diff --git a/LEGO1/legostream.h b/LEGO1/legostream.h
index 899bd7e1..a505cd54 100644
--- a/LEGO1/legostream.h
+++ b/LEGO1/legostream.h
@@ -9,6 +9,7 @@
 #define LEGOSTREAM_MODE_READ 1
 #define LEGOSTREAM_MODE_WRITE 2
 
+// VTABLE 0x100d7d80
 class LegoStream
 {
 public:
@@ -34,6 +35,7 @@ class LegoStream
   MxU8 m_mode;
 };
 
+// VTABLE 0x100db730
 class LegoFileStream : public LegoStream
 {
 public:
@@ -51,6 +53,7 @@ class LegoFileStream : public LegoStream
   FILE *m_hFile;
 };
 
+// VTABLE 0x100db710
 class LegoMemoryStream : public LegoStream
 {
 public: