diff --git a/stepmania/src/RageFile.cpp b/stepmania/src/RageFile.cpp
index 15b4d59ae4..af19772d14 100644
--- a/stepmania/src/RageFile.cpp
+++ b/stepmania/src/RageFile.cpp
@@ -333,7 +333,9 @@ int RageFile::GetFileSize() const
 	/* GetFileSize() may need to do non-const-like things--the default implementation reads
 	 * until the end of file to emulate it.  However, it should always restore the state to
 	 * the way it was, so pretend it's const. */
-	return const_cast<RageFileObj*>(m_File)->GetFileSize();
+	int iRet = const_cast<RageFileObj*>(m_File)->GetFileSize();
+	ASSERT_M( iRet >= 0, ssprintf("%i", iRet) );
+	return iRet;
 }
 
 void RageFile::Rewind()
@@ -342,7 +344,7 @@ void RageFile::Rewind()
 		RageException::Throw("\"%s\" is not open.", GetPath().c_str());
 
 	if( !(m_Mode&READ) )
-		RageException::Throw("\"%s\" is not open for reading; can't GetFileSize", GetPath().c_str());
+		RageException::Throw("\"%s\" is not open for reading; can't Rewind", GetPath().c_str());
 
 	m_EOF = false;
 
diff --git a/stepmania/src/RageFileDriverDirect.cpp b/stepmania/src/RageFileDriverDirect.cpp
index 086a4afb5a..d37d3b59e9 100644
--- a/stepmania/src/RageFileDriverDirect.cpp
+++ b/stepmania/src/RageFileDriverDirect.cpp
@@ -372,7 +372,9 @@ int RageFileObjDirect::Seek( int offset )
 int RageFileObjDirect::GetFileSize()
 {
 	const int OldPos = lseek( fd, 0, SEEK_CUR );
+	ASSERT_M( OldPos != -1, strerror(errno) ):
 	const int ret = lseek( fd, 0, SEEK_END );
+	ASSERT_M( ret!= -1, strerror(errno) ):
 	lseek( fd, OldPos, SEEK_SET );
 	return ret;
 }