diff --git a/kernel/dosfns.c b/kernel/dosfns.c
index 7fbd112e..8d214888 100644
--- a/kernel/dosfns.c
+++ b/kernel/dosfns.c
@@ -501,6 +501,44 @@ const char FAR *get_basename(__XFAR(const char)fname)
   return fname;
 }
 
+/* Extracts the device name from a path for IsDevice() validation.
+ * Preserves names with an optional trailing colon, while leaving
+ * bare drive specifications untouched.
+ *
+ * Examples:
+ *   "NUL:"         -> "NUL:"
+ *   "C:\DIR\NUL:"  -> "NUL:"
+ *   "C:NUL:"       -> "NUL:"
+ *   "NUL"          -> "NUL"
+ *   "C:"           -> ""
+ *   "C:\DIR\FILE"  -> "FILE"
+ */
+const char FAR *get_devname(__XFAR(const char) fname)
+{
+  const char FAR *froot = get_basename(fname);
+  const char FAR *name_start;
+
+  /* If a valid basename was found, or the path doesn't end in ':', we're done */
+  if (*froot != '\0' || froot == fname || *(froot - 1) != ':')
+    return froot;
+
+  /* Walk back before the trailing ':' to find the start of the device token */
+  name_start = froot - 1;
+  while (name_start > fname &&
+         name_start[-1] != '/' &&
+         name_start[-1] != '\\' &&
+         name_start[-1] != ':')
+  {
+    name_start--;
+  }
+
+  /* Single-character prefixes before the colon (e.g., "C:") are bare drive specs */
+  if ((froot - 1) - name_start < 2)
+    return froot;
+
+  return name_start;
+}
+
 STATIC void ConvertPathNameToFCBName(char *FCBName, const char FAR *PathName)
 {
   ConvertNameSZToName83(FCBName, get_basename(PathName));
@@ -1423,7 +1461,7 @@ COUNT DosLockUnlock(COUNT hndl, LONG pos, LONG len, COUNT unlock)
 struct dhdr FAR *IsDevice(__XFAR(const char)fname)
 {
   struct dhdr FAR *dhp;
-  const char FAR *froot = get_basename(fname);
+  const char FAR *froot = get_devname(fname);
   int i;
 
 /* /// BUG!!! This is absolutely wrong.  A filename of "NUL.LST" must be
@@ -1464,8 +1502,9 @@ struct dhdr FAR *IsDevice(__XFAR(const char)fname)
     for (i = 0; i < FNAME_SIZE; i++)
     {
       unsigned char c1 = (unsigned char)froot[i];
-      /* ignore extensions and handle filenames shorter than FNAME_SIZE */
-      if (c1 == '.' || c1 == '\0')
+      /* ignore extensions and handle filenames shorter than FNAME_SIZE;
+         a trailing colon ("NUL:") also ends the name */
+      if (c1 == '.' || c1 == '\0' || c1 == ':')
       {
         /* check if remainder of device name consists of spaces or nulls */
         for (; i < FNAME_SIZE; i++)
diff --git a/kernel/newstuff.c b/kernel/newstuff.c
index 221bf394..61760edb 100644
--- a/kernel/newstuff.c
+++ b/kernel/newstuff.c
@@ -373,7 +373,7 @@ COUNT truename(__XFAR(const char) src, char FAR *dest, COUNT mode)
   dest[2] = '\\';
   if (result & IS_DEVICE)
   {
-    froot = get_basename(src);
+    froot = get_devname(src);
     if (froot == src || froot == src + 5)
     {
       if (froot == src + 5)
@@ -528,6 +528,9 @@ COUNT truename(__XFAR(const char) src, char FAR *dest, COUNT mode)
     while(*src != '/' && *src  != '\\' && *src != '\0')
     {
       char c = *src++;
+      /* "NUL:" - ignore the colon that follows a device name */
+      if (c == ':' && *src == '\0' && (result & IS_DEVICE))
+        break;
       if (c == '*')
       {
         /* register the wildcard, even if no '?' is appended */
diff --git a/kernel/proto.h b/kernel/proto.h
index 55f41e40..52077788 100644
--- a/kernel/proto.h
+++ b/kernel/proto.h
@@ -82,6 +82,7 @@ __FAR(sft)get_sft(UCOUNT);
 
 /* dosfns.c */
 __FAR(const char)get_basename(__XFAR(const char));
+__FAR(const char)get_devname(__XFAR(const char));
 BOOL check_break(void);
 UCOUNT GenericReadSft(__FAR(sft) sftp, UCOUNT n,__FAR(void) bp,
                       COUNT * err, BOOL force_binary);