diff --git a/base/changes.txt b/base/changes.txt
index c00b2351e..c6da05755 100644
--- a/base/changes.txt
+++ b/base/changes.txt
@@ -13,6 +13,12 @@ not part of the distribution.
 	\index entries that are used directly in the document and aren't hidden
 	inside other macros (because then no expansion happens) gh/1418
 
+2024-12-23  Frank Mittelbach  <Frank.Mittelbach@latex-project.org>
+
+	* docstrip.dtx (subsection{Batchfile commands}):
+	Check that the stream macro (with the name of a file to generate) is not
+	already used, e.g., as a declared preamble (gh/1150)
+
 2024-12-22  Frank Mittelbach  <Frank.Mittelbach@latex-project.org>
 
 	* ltcmdhooks.dtx (subsection{Patching or delaying}):
diff --git a/base/doc/ltnews41.tex b/base/doc/ltnews41.tex
index 2a5abf5c1..fbe8cac83 100644
--- a/base/doc/ltnews41.tex
+++ b/base/doc/ltnews41.tex
@@ -370,6 +370,18 @@ \subsection{Fix the use of  \texttt{localmathalpabets}}
 %
 \githubissue[s]{1101 1028}
 
+\subsection{\pkg{docstrip}:\ Error if \texttt{.ins} file is problematical}
+
+If a file to generate had the same name as a preamble declared with
+\cs{declarepreamble} the preamble definition was overwritten because
+the macro used to store it was reused for denoting the output
+stream. The same problem happened with postambles declared with
+\cs{declarepostamble}. This is now detected and an error message is
+issued. To circumvent the issue in that case, simply use a different
+macro name for the preamble or postamble.
+%
+\githubissue{1150}
+
 
 \subsection{Prevent \texttt{cmd} hook from defining an undefined command}
 
diff --git a/base/docstrip.dtx b/base/docstrip.dtx
index 1d61d78f5..72ce24f5b 100644
--- a/base/docstrip.dtx
+++ b/base/docstrip.dtx
@@ -29,9 +29,9 @@
 \catcode`\{=1
 \catcode`\}=2
 \def\filename{docstrip.dtx}
-\def\fileversion{v2.6b}
-\def\filedate{2022-09-03}
-\def\docdate {2024-02-08}
+\def\fileversion{v2.6c}
+\def\filedate{2024-12-23}
+\def\docdate {2024-12-23}
 %%
 %
 %\iffalse
@@ -3027,8 +3027,37 @@ Z
 %    defining preamble for the current file.
 %    \begin{macrocode}
 \def\@fileX#1#2{%
+%    \end{macrocode}
+%    If the csname used for the stream has already been defined, e.g.,
+%    as a preamble or postamble or for some other purposes, chances are
+%    that turning it into a stream number will break something. We
+%    therefore generate an error and show the current definition.
+% \changes{v2.6c}{2024-12-23}{Check that stream macro is not already
+%    used (gh/1150)}
+%    \begin{macrocode}
+  \ifx#1\relax \else
+     \errmessage{Command \string#1 for denoting the output \noexpand
+       \file stream already defined!^^J
+       \space Current meaning is:^^J^^J\meaning#1^^J^^J
+       \space Extraction will probably fail - check result}%
+  \fi
   \chardef#1=\stream@closed
   \def\curout{#1}%
+%    \end{macrocode}
+%    If it matches the name of the current preamble or postamble then
+%    it definitely can't work, so we call that out explicitly:
+%    \begin{macrocode}
+  \ifx\curout\currentpreamble
+     \errmessage{Declared preamble name \string#1 not allowed if
+       \string\file{\@stripstring#1} is used}%
+  \fi
+  \ifx\curout\currentpostamble
+     \errmessage{Declared postamble name \string#1 not allowed if
+       \string\file{\@stripstring#1} is used}%
+  \fi
+%    \end{macrocode}
+%
+%    \begin{macrocode}
   \let\curinfiles\empty
   \let\curinnames\empty
   \def\curref{\MetaPrefix ^^J%