diff --git a/src/structs.h b/src/structs.h
index 75ad127..d6763ab 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4422,3 +4422,6 @@ typedef struct {
     char    wt_variable;    // "variable" when TRUE, "argument" otherwise
 } where_T;
 
+// Return the length of a string literal
+#define STRLEN_LITERAL(s) (sizeof(s) - 1)
+
diff --git a/src/tag.c b/src/tag.c
index 37ed66c..c305f25 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -2912,7 +2912,7 @@ get_tagfname(
 	    if (tnp->tn_hf_idx > tag_fnames.ga_len || *p_hf == NUL)
 		return FAIL;
 	    ++tnp->tn_hf_idx;
-	    STRCPY(buf, p_hf);
+	    vim_strncpy(buf, p_hf, MAXPATHL - 1);
 	    STRCPY(gettail(buf), "tags");
 #ifdef BACKSLASH_IN_FILENAME
 	    slash_adjust(buf);
diff --git a/src/testdir/test_help.vim b/src/testdir/test_help.vim
index c8ff5b8..6a45194 100644
--- a/src/testdir/test_help.vim
+++ b/src/testdir/test_help.vim
@@ -131,5 +131,13 @@ func Test_help_long_argument()
   endtry
 endfunc
 
+" This caused a buffer overflow
+func Test_helpfile_overflow()
+  let _helpfile = &helpfile
+  let &helpfile = repeat('A', 5000)
+  help
+  helpclose
+  let &helpfile = _helpfile
+endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab