diff --git a/src/MatroskaParser.c b/src/MatroskaParser.c
index 176d136482..9983911af7 100644
--- a/src/MatroskaParser.c
+++ b/src/MatroskaParser.c
@@ -2250,7 +2250,7 @@ static void parseBlockGroup(MatroskaFile *mf,uint64_t toplen,uint64_t timecode,
 
       // we want to still load these bytes into cache
       for (v = filepos(mf) & ~0x3fff; v < len + dpos; v += 0x4000)
-	mf->cache->read(mf->cache,v,NULL,0); // touch page
+	mf->cache->read(mf->cache,v,NULL,0); // touch page (FIXME this doesn't really do anything)
 
       skipbytes(mf,len - filepos(mf) + dpos);
 
diff --git a/src/mkv_wrap.cpp b/src/mkv_wrap.cpp
index 9eed3b704e..e0f69972a4 100644
--- a/src/mkv_wrap.cpp
+++ b/src/mkv_wrap.cpp
@@ -69,8 +69,13 @@ struct MkvStdIO final : InputStream {
 		if (remaining < INT_MAX)
 			count = std::min(static_cast<int>(remaining), count);
 
+		if (count <= 0)
+			return 0;
+
 		try {
-			memcpy(buffer, self->file.read(pos, count), count);
+			auto data = self->file.read(pos, count);
+			if (buffer)
+				memcpy(buffer, data, count);
 		}
 		catch (agi::Exception const& e) {
 			self->error = e.GetMessage();