diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index ce1ab34..d6a7854 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1,5 +1,7 @@
 " Test various aspects of the Vim9 script language.
 
+source check.vim
+
 " Check that "lines" inside ":def" results in an "error" message.
 func CheckDefFailure(lines, error)
   call writefile(['def! Func()'] + a:lines + ['enddef'], 'Xdef')
@@ -355,5 +357,16 @@
   call assert_equal([2, 99, 3, 4, 5], l)
 enddef
 
+" Test that inside :function a Python function can be defined, :def is not
+" recognized.
+func Test_function_python()
+  CheckFeature python3
+  let py = 'python3'
+  execute py "<< EOF"
+def do_something():
+  return 1
+EOF
+endfunc
+
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/userfunc.c b/src/userfunc.c
index 808ed96..ce776ee 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -2667,8 +2667,11 @@
 		indent += 2;
 
 	    // Check for defining a function inside this function.
+	    // Only recognize "def" inside "def", not inside "function",
+	    // For backwards compatibility, see Test_function_python().
 	    c = *p;
-	    if (checkforcmd(&p, "function", 2) || checkforcmd(&p, "def", 3))
+	    if (checkforcmd(&p, "function", 2)
+		    || (eap->cmdidx == CMD_def && checkforcmd(&p, "def", 3)))
 	    {
 		if (*p == '!')
 		    p = skipwhite(p + 1);
diff --git a/src/version.c b/src/version.c
index 3b4a959..159d550 100644
--- a/src/version.c
+++ b/src/version.c
@@ -743,6 +743,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    150,
+/**/
     149,
 /**/
     148,