diff --git a/src/eval.c b/src/eval.c
index 1f43970..77f0d7f 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -253,7 +253,7 @@
 	    if (fc == NULL)
 		return FAIL;
 
-	    // Shortcut to call a compiled function without overhead.
+	    // Shortcut to call a compiled function with minimal overhead.
 	    r = call_def_function(partial->pt_func, argc, argv,
 					  DEF_USE_PT_ARGV, partial, fc, rettv);
 	    remove_funccal();
@@ -2291,7 +2291,7 @@
 
 	if (next != NULL)
 	{
-	    *getnext = TRUE;
+	    *getnext = *p != NL;
 	    return skipwhite(next);
 	}
     }
diff --git a/src/testdir/test_source.vim b/src/testdir/test_source.vim
index 44cd2fd..2becf08 100644
--- a/src/testdir/test_source.vim
+++ b/src/testdir/test_source.vim
@@ -665,5 +665,22 @@
   call delete('Xtest.vim')
 endfunc
 
+func Test_source_buffer_with_NUL_char()
+  " This was trying to use a line below the buffer.
+  let lines =<< trim END
+      if !exists('g:loaded')
+        let g:loaded = 1
+        source
+      endif
+  END
+  " Can't have a NL in heredoc
+  let lines += ["silent! vim9 echo [0 \<NL> ? 'a' : 'b']"]
+  call writefile(lines, 'XsourceNul', '')
+  edit XsourceNul
+  source
+
+  bwipe!
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index c3b6c12..505185d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    552,
+/**/
     551,
 /**/
     550,