diff --git a/src/physfs.c b/src/physfs.c
index 9ea904b..992ae31 100644
--- a/src/physfs.c
+++ b/src/physfs.c
@@ -1012,6 +1012,8 @@ static DirHandle *createDirHandle(PHYSFS_Io *io, const char *newDir,
     DirHandle *dirHandle = NULL;
     char *tmpmntpnt = NULL;
 
+    assert(newDir != NULL);  /* should have caught this higher up. */
+
     if (mountPoint != NULL)
     {
         const size_t len = strlen(mountPoint) + 1;
@@ -1025,15 +1027,9 @@ static DirHandle *createDirHandle(PHYSFS_Io *io, const char *newDir,
     dirHandle = openDirectory(io, newDir, forWriting);
     GOTO_IF_ERRPASS(!dirHandle, badDirHandle);
 
-    if (newDir == NULL)
-        dirHandle->dirName = NULL;
-    else
-    {
-        dirHandle->dirName = (char *) allocator.Malloc(strlen(newDir) + 1);
-        if (!dirHandle->dirName)
-            GOTO(PHYSFS_ERR_OUT_OF_MEMORY, badDirHandle);
-        strcpy(dirHandle->dirName, newDir);
-    } /* else */
+    dirHandle->dirName = (char *) allocator.Malloc(strlen(newDir) + 1);
+    GOTO_IF(!dirHandle->dirName, PHYSFS_ERR_OUT_OF_MEMORY, badDirHandle);
+    strcpy(dirHandle->dirName, newDir);
 
     if ((mountPoint != NULL) && (*mountPoint != '\0'))
     {
@@ -1684,21 +1680,20 @@ static int doMount(PHYSFS_Io *io, const char *fname,
     DirHandle *prev = NULL;
     DirHandle *i;
 
+    BAIL_IF(!fname, PHYSFS_ERR_INVALID_ARGUMENT, 0);
+
     if (mountPoint == NULL)
         mountPoint = "/";
 
     __PHYSFS_platformGrabMutex(stateLock);
 
-    if (fname != NULL)
+    for (i = searchPath; i != NULL; i = i->next)
     {
-        for (i = searchPath; i != NULL; i = i->next)
-        {
-            /* already in search path? */
-            if ((i->dirName != NULL) && (strcmp(fname, i->dirName) == 0))
-                BAIL_MUTEX_ERRPASS(stateLock, 1);
-            prev = i;
-        } /* for */
-    } /* if */
+        /* already in search path? */
+        if ((i->dirName != NULL) && (strcmp(fname, i->dirName) == 0))
+            BAIL_MUTEX_ERRPASS(stateLock, 1);
+        prev = i;
+    } /* for */
 
     dh = createDirHandle(io, fname, mountPoint, 0);
     BAIL_IF_MUTEX_ERRPASS(!dh, stateLock, 0);
@@ -1725,6 +1720,7 @@ int PHYSFS_mountIo(PHYSFS_Io *io, const char *fname,
                    const char *mountPoint, int appendToPath)
 {
     BAIL_IF(!io, PHYSFS_ERR_INVALID_ARGUMENT, 0);
+    BAIL_IF(!fname, PHYSFS_ERR_INVALID_ARGUMENT, 0);
     BAIL_IF(io->version != 0, PHYSFS_ERR_UNSUPPORTED, 0);
     return doMount(io, fname, mountPoint, appendToPath);
 } /* PHYSFS_mountIo */
@@ -1738,6 +1734,7 @@ int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len, void (*del)(void *),
     PHYSFS_Io *io = NULL;
 
     BAIL_IF(!buf, PHYSFS_ERR_INVALID_ARGUMENT, 0);
+    BAIL_IF(!fname, PHYSFS_ERR_INVALID_ARGUMENT, 0);
 
     io = __PHYSFS_createMemoryIo(buf, len, del);
     BAIL_IF_ERRPASS(!io, 0);
@@ -1760,7 +1757,8 @@ int PHYSFS_mountHandle(PHYSFS_File *file, const char *fname,
     int retval = 0;
     PHYSFS_Io *io = NULL;
 
-    BAIL_IF(file == NULL, PHYSFS_ERR_INVALID_ARGUMENT, 0);
+    BAIL_IF(!file, PHYSFS_ERR_INVALID_ARGUMENT, 0);
+    BAIL_IF(!fname, PHYSFS_ERR_INVALID_ARGUMENT, 0);
 
     io = __PHYSFS_createHandleIo(file);
     BAIL_IF_ERRPASS(!io, 0);
@@ -1785,7 +1783,7 @@ int PHYSFS_mount(const char *newDir, const char *mountPoint, int appendToPath)
 
 int PHYSFS_addToSearchPath(const char *newDir, int appendToPath)
 {
-    return doMount(NULL, newDir, NULL, appendToPath);
+    return PHYSFS_mount(newDir, NULL, appendToPath);
 } /* PHYSFS_addToSearchPath */
 
 
diff --git a/src/physfs.h b/src/physfs.h
index 1abd2b0..e9ef93d 100644
--- a/src/physfs.h
+++ b/src/physfs.h
@@ -2760,6 +2760,12 @@ PHYSFS_DECL int PHYSFS_enumerate(const char *dir, PHYSFS_EnumerateCallback c,
  * This call will fail (and fail to remove from the path) if the element still
  *  has files open in it.
  *
+ * \warning This function wants the path to the archive or directory that was
+ *          mounted (the same string used for the "newDir" argument of
+ *          PHYSFS_addToSearchPath or any of the mount functions), not the
+ *          path where it is mounted in the tree (the "mountPoint" argument
+ *          to any of the mount functions).
+ *
  *    \param oldDir dir/archive to remove.
  *   \return nonzero on success, zero on failure. Use
  *           PHYSFS_getLastErrorCode() to obtain the specific error.
@@ -3188,7 +3194,7 @@ typedef struct PHYSFS_Io
 
 
 /**
- * \fn int PHYSFS_mountIo(PHYSFS_Io *io, const char *fname, const char *mountPoint, int appendToPath)
+ * \fn int PHYSFS_mountIo(PHYSFS_Io *io, const char *newDir, const char *mountPoint, int appendToPath)
  * \brief Add an archive, built on a PHYSFS_Io, to the search path.
  *
  * \warning Unless you have some special, low-level need, you should be using
@@ -3198,11 +3204,14 @@ typedef struct PHYSFS_Io
  *  instead of a pathname. Behind the scenes, PHYSFS_mount() calls this
  *  function with a physical-filesystem-based PHYSFS_Io.
  *
- * (filename) is only used here to optimize archiver selection (if you name it
- *  XXXXX.zip, we might try the ZIP archiver first, for example). It doesn't
- *  need to refer to a real file at all, and can even be NULL. If the filename
- *  isn't helpful, the system will try every archiver until one works or none
- *  of them do.
+ * (newDir) must be a unique string to identify this archive. It is used
+ *  to optimize archiver selection (if you name it XXXXX.zip, we might try
+ *  the ZIP archiver first, for example, or directly choose an archiver that
+ *  can only trust the data is valid by filename extension). It doesn't
+ *  need to refer to a real file at all. If the filename extension isn't
+ *  helpful, the system will try every archiver until one works or none
+ *  of them do. This filename must be unique, as the system won't allow you
+ *  to have two archives with the same name.
  *
  * (io) must remain until the archive is unmounted. When the archive is
  *  unmounted, the system will call (io)->destroy(io), which will give you
@@ -3211,7 +3220,7 @@ typedef struct PHYSFS_Io
  * If this function fails, (io)->destroy(io) is not called.
  *
  *   \param io i/o instance for archive to add to the path.
- *   \param fname Filename that can represent this stream. Can be NULL.
+ *   \param newDir Filename that can represent this stream.
  *   \param mountPoint Location in the interpolated tree that this archive
  *                     will be "mounted", in platform-independent notation.
  *                     NULL or "" is equivalent to "/".
@@ -3224,12 +3233,12 @@ typedef struct PHYSFS_Io
  * \sa PHYSFS_getSearchPath
  * \sa PHYSFS_getMountPoint
  */
-PHYSFS_DECL int PHYSFS_mountIo(PHYSFS_Io *io, const char *fname,
+PHYSFS_DECL int PHYSFS_mountIo(PHYSFS_Io *io, const char *newDir,
                                const char *mountPoint, int appendToPath);
 
 
 /**
- * \fn int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len, void (*del)(void *), const char *fname, const char *mountPoint, int appendToPath)
+ * \fn int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len, void (*del)(void *), const char *newDir, const char *mountPoint, int appendToPath)
  * \brief Add an archive, contained in a memory buffer, to the search path.
  *
  * \warning Unless you have some special, low-level need, you should be using
@@ -3239,11 +3248,14 @@ PHYSFS_DECL int PHYSFS_mountIo(PHYSFS_Io *io, const char *fname,
  *  instead of a pathname. This buffer contains all the data of the archive,
  *  and is used instead of a real file in the physical filesystem.
  *
- * (filename) is only used here to optimize archiver selection (if you name it
- *  XXXXX.zip, we might try the ZIP archiver first, for example). It doesn't
- *  need to refer to a real file at all, and can even be NULL. If the filename
- *  isn't helpful, the system will try every archiver until one works or none
- *  of them do.
+ * (newDir) must be a unique string to identify this archive. It is used
+ *  to optimize archiver selection (if you name it XXXXX.zip, we might try
+ *  the ZIP archiver first, for example, or directly choose an archiver that
+ *  can only trust the data is valid by filename extension). It doesn't
+ *  need to refer to a real file at all. If the filename extension isn't
+ *  helpful, the system will try every archiver until one works or none
+ *  of them do. This filename must be unique, as the system won't allow you
+ *  to have two archives with the same name.
  *
  * (ptr) must remain until the archive is unmounted. When the archive is
  *  unmounted, the system will call (del)(ptr), which will notify you that
@@ -3256,7 +3268,7 @@ PHYSFS_DECL int PHYSFS_mountIo(PHYSFS_Io *io, const char *fname,
  *   \param buf Address of the memory buffer containing the archive data.
  *   \param len Size of memory buffer, in bytes.
  *   \param del A callback that triggers upon unmount. Can be NULL.
- *   \param fname Filename that can represent this stream. Can be NULL.
+ *   \param newDir Filename that can represent this stream.
  *   \param mountPoint Location in the interpolated tree that this archive
  *                     will be "mounted", in platform-independent notation.
  *                     NULL or "" is equivalent to "/".
@@ -3269,12 +3281,12 @@ PHYSFS_DECL int PHYSFS_mountIo(PHYSFS_Io *io, const char *fname,
  * \sa PHYSFS_getMountPoint
  */
 PHYSFS_DECL int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len,
-                                   void (*del)(void *), const char *fname,
+                                   void (*del)(void *), const char *newDir,
                                    const char *mountPoint, int appendToPath);
 
 
 /**
- * \fn int PHYSFS_mountHandle(PHYSFS_File *file, const char *fname, const char *mountPoint, int appendToPath)
+ * \fn int PHYSFS_mountHandle(PHYSFS_File *file, const char *newDir, const char *mountPoint, int appendToPath)
  * \brief Add an archive, contained in a PHYSFS_File handle, to the search path.
  *
  * \warning Unless you have some special, low-level need, you should be using
@@ -3297,11 +3309,14 @@ PHYSFS_DECL int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len,
  *  but isn't necessarily. The most popular use for this is likely to mount
  *  archives stored inside other archives.
  *
- * (filename) is only used here to optimize archiver selection (if you name it
- *  XXXXX.zip, we might try the ZIP archiver first, for example). It doesn't
- *  need to refer to a real file at all, and can even be NULL. If the filename
- *  isn't helpful, the system will try every archiver until one works or none
- *  of them do.
+ * (newDir) must be a unique string to identify this archive. It is used
+ *  to optimize archiver selection (if you name it XXXXX.zip, we might try
+ *  the ZIP archiver first, for example, or directly choose an archiver that
+ *  can only trust the data is valid by filename extension). It doesn't
+ *  need to refer to a real file at all. If the filename extension isn't
+ *  helpful, the system will try every archiver until one works or none
+ *  of them do. This filename must be unique, as the system won't allow you
+ *  to have two archives with the same name.
  *
  * (file) must remain until the archive is unmounted. When the archive is
  *  unmounted, the system will call PHYSFS_close(file). If you need this
@@ -3311,7 +3326,7 @@ PHYSFS_DECL int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len,
  * If this function fails, PHYSFS_close(file) is not called.
  *
  *   \param file The PHYSFS_File handle containing archive data.
- *   \param fname Filename that can represent this stream. Can be NULL.
+ *   \param newDir Filename that can represent this stream.
  *   \param mountPoint Location in the interpolated tree that this archive
  *                     will be "mounted", in platform-independent notation.
  *                     NULL or "" is equivalent to "/".
@@ -3323,7 +3338,7 @@ PHYSFS_DECL int PHYSFS_mountMemory(const void *buf, PHYSFS_uint64 len,
  * \sa PHYSFS_getSearchPath
  * \sa PHYSFS_getMountPoint
  */
-PHYSFS_DECL int PHYSFS_mountHandle(PHYSFS_File *file, const char *fname,
+PHYSFS_DECL int PHYSFS_mountHandle(PHYSFS_File *file, const char *newDir,
                                    const char *mountPoint, int appendToPath);