diff --git a/addons/acodec/modaudio.c b/addons/acodec/modaudio.c
index 7ef963cb42..9510d21424 100644
--- a/addons/acodec/modaudio.c
+++ b/addons/acodec/modaudio.c
@@ -59,13 +59,21 @@ static bool libdumb_loaded = false;
 static void *dumb_dll = NULL;
 #endif
 
+/*
+ * DUMB_OFF_T is introduced in DUMB 2.0, it's a signed 64+ bit integer.
+ * DUMB 0.9.3 expects long wherever DUMB_OFF_T appears in the DUMB 2.0 API.
+ */
+#ifndef DUMB_OFF_T
+#define DUMB_OFF_T long
+#endif
+
 static struct
 {
    long (*duh_sigrenderer_get_position)(DUH_SIGRENDERER *);
    void (*duh_end_sigrenderer)(DUH_SIGRENDERER *);
    void (*unload_duh)(DUH *);
    DUH_SIGRENDERER *(*duh_start_sigrenderer)(DUH *, int, int, long);
-   long (*duh_get_length)(DUH *);
+   DUMB_OFF_T (*duh_get_length)(DUH *);
    void (*dumb_exit)(void);
    DUMB_IT_SIGRENDERER *(*duh_get_it_sigrenderer)(DUH_SIGRENDERER *);
    void (*dumb_it_set_loop_callback)(DUMB_IT_SIGRENDERER *, int (*)(void *), void *);
@@ -76,10 +84,12 @@ static struct
    /*
     * DUMB 2.0 deprecates duh_render, and suggests instead duh_render_int
     * and duh_render_float. But I (Simon N.) don't know how to use those.
+    * I have already written some documentation for DUMB 2.0 that got merged
+    * upstream, but I haven't gotten around to this issue yet.
     */
    long (*duh_render)(DUH_SIGRENDERER *,
-      int, int, float, float, long, void *);
-    void (*register_dumbfile_system)(const DUMBFILE_SYSTEM *);
+      int, int, float, float, long, void *); /* deprecated */
+   void (*register_dumbfile_system)(const DUMBFILE_SYSTEM *);
    DUMBFILE *(*dumbfile_open_ex)(void *, const DUMBFILE_SYSTEM *);
    DUH *(*dumb_read_any)(DUMBFILE *, int, int);
 #else
@@ -102,7 +112,7 @@ static void *dfs_open(const char *filename)
    return al_fopen(filename, "rb");
 }
 
-static int dfs_skip(void *f, long n)
+static int dfs_skip(void *f, DUMB_OFF_T n)
 {
    return al_fseek(f, n, ALLEGRO_SEEK_CUR) ? 0 : -1;
 }
@@ -112,7 +122,7 @@ static int dfs_getc(void *f)
    return al_fgetc(f);
 }
 
-static long dfs_getnc(char *ptr, long n, void *f)
+static DUMB_OFF_T dfs_getnc(char *ptr, DUMB_OFF_T n, void *f)
 {
    return al_fread(f, ptr, n);
 }
@@ -124,12 +134,12 @@ static void dfs_close(void *f)
 }
 
 #if (DUMB_MAJOR_VERSION) >= 2
-static int dfs_seek(void *f, long n)
+static int dfs_seek(void *f, DUMB_OFF_T n)
 {
    return al_fseek(f, n, ALLEGRO_SEEK_SET) ? 0 : -1;
 }
 
-static long dfs_get_size(void *f)
+static DUMB_OFF_T dfs_get_size(void *f)
 {
    return al_fsize(f);
 }