diff --git a/src/base/system.cpp b/src/base/system.cpp
index 491421c30..2437a06aa 100644
--- a/src/base/system.cpp
+++ b/src/base/system.cpp
@@ -283,6 +283,7 @@ void mem_zero(void *block, unsigned size)
 
 IOHANDLE io_open(const char *filename, int flags)
 {
+	dbg_assert(flags == IOFLAG_READ || flags == IOFLAG_WRITE || flags == IOFLAG_APPEND, "flags must be read, write or append");
 	if(flags == IOFLAG_READ)
 		return (IOHANDLE)fopen(filename, "rb");
 	if(flags == IOFLAG_WRITE)
diff --git a/src/base/system.h b/src/base/system.h
index fe516f047..c13c61407 100644
--- a/src/base/system.h
+++ b/src/base/system.h
@@ -170,8 +170,7 @@ enum
 {
 	IOFLAG_READ = 1,
 	IOFLAG_WRITE = 2,
-	IOFLAG_RANDOM = 4,
-	IOFLAG_APPEND = 8,
+	IOFLAG_APPEND = 4,
 
 	IOSEEK_START = 0,
 	IOSEEK_CUR = 1,
@@ -186,7 +185,7 @@ typedef struct IOINTERNAL *IOHANDLE;
 
 	Parameters:
 		filename - File to open.
-		flags - A set of flags. IOFLAG_READ, IOFLAG_WRITE, IOFLAG_RANDOM, IOFLAG_APPEND.
+		flags - A set of flags. IOFLAG_READ, IOFLAG_WRITE, IOFLAG_APPEND.
 
 	Returns:
 		Returns a handle to the file on success and 0 on failure.