diff --git a/Documentation/technical/api-setup.txt b/Documentation/technical/api-setup.txt
index 90d1aff625..540e455689 100644
--- a/Documentation/technical/api-setup.txt
+++ b/Documentation/technical/api-setup.txt
@@ -28,3 +28,22 @@ parse_pathspec(). This function takes several arguments:
 - prefix and args come from cmd_* functions
 
 get_pathspec() is obsolete and should never be used in new code.
+
+parse_pathspec() helps catch unsupported features and reject them
+politely. At a lower level, different pathspec-related functions may
+not support the same set of features. Such pathspec-sensitive
+functions are guarded with GUARD_PATHSPEC(), which will die in an
+unfriendly way when an unsupported feature is requested.
+
+The command designers are supposed to make sure that GUARD_PATHSPEC()
+never dies. They have to make sure all unsupported features are caught
+by parse_pathspec(), not by GUARD_PATHSPEC. grepping GUARD_PATHSPEC()
+should give the designers all pathspec-sensitive codepaths and what
+features they support.
+
+A similar process is applied when a new pathspec magic is added. The
+designer lifts the GUARD_PATHSPEC restriction in the functions that
+support the new magic. At the same time (s)he has to make sure this
+new feature will be caught at parse_pathspec() in commands that cannot
+handle the new magic in some cases. grepping parse_pathspec() should
+help.
diff --git a/builtin/diff.c b/builtin/diff.c
index 9fc273d8cd..6bb41aff5d 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -367,6 +367,8 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		}
 	}
 	if (rev.prune_data.nr) {
+		/* builtin_diff_b_f() */
+		GUARD_PATHSPEC(&rev.prune_data, PATHSPEC_FROMTOP);
 		if (!path)
 			path = rev.prune_data.items[0].match;
 		paths += rev.prune_data.nr;
diff --git a/dir.c b/dir.c
index e28bc0d636..19978d3d59 100644
--- a/dir.c
+++ b/dir.c
@@ -340,6 +340,8 @@ int match_pathspec_depth(const struct pathspec *ps,
 {
 	int i, retval = 0;
 
+	GUARD_PATHSPEC(ps, PATHSPEC_FROMTOP | PATHSPEC_MAXDEPTH);
+
 	if (!ps->nr) {
 		if (!ps->recursive ||
 		    !(ps->magic & PATHSPEC_MAXDEPTH) ||
diff --git a/pathspec.h b/pathspec.h
index 2e427d7f4c..6baf205862 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -27,6 +27,13 @@ struct pathspec {
 	} *items;
 };
 
+#define GUARD_PATHSPEC(ps, mask) \
+	do { \
+		if ((ps)->magic & ~(mask))	       \
+			die("BUG:%s:%d: unsupported magic %x",	\
+			    __FILE__, __LINE__, (ps)->magic & ~(mask)); \
+	} while (0)
+
 /* parse_pathspec flags */
 #define PATHSPEC_PREFER_CWD (1<<0) /* No args means match cwd */
 #define PATHSPEC_PREFER_FULL (1<<1) /* No args means match everything */
diff --git a/tree-diff.c b/tree-diff.c
index 826512e84d..5a876148bb 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -198,6 +198,25 @@ static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, co
 	const char *paths[1];
 	int i;
 
+	/*
+	 * follow-rename code is very specific, we need exactly one
+	 * path. Magic that matches more than one path is not
+	 * supported.
+	 */
+	GUARD_PATHSPEC(&opt->pathspec, PATHSPEC_FROMTOP);
+#if 0
+	/*
+	 * We should reject wildcards as well. Unfortunately we
+	 * haven't got a reliable way to detect that 'foo\*bar' in
+	 * fact has no wildcards. nowildcard_len is merely a hint for
+	 * optimization. Let it slip for now until wildmatch is taught
+	 * about dry-run mode and returns wildcard info.
+	 */
+	if (opt->pathspec.has_wildcard)
+		die("BUG:%s:%d: wildcards are not supported",
+		    __FILE__, __LINE__);
+#endif
+
 	/* Remove the file creation entry from the diff queue, and remember it */
 	choice = q->queue[0];
 	q->nr = 0;
diff --git a/tree-walk.c b/tree-walk.c
index d399ca9dcc..37b157ed6e 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -636,6 +636,8 @@ enum interesting tree_entry_interesting(const struct name_entry *entry,
 	enum interesting never_interesting = ps->has_wildcard ?
 		entry_not_interesting : all_entries_not_interesting;
 
+	GUARD_PATHSPEC(ps, PATHSPEC_FROMTOP | PATHSPEC_MAXDEPTH);
+
 	if (!ps->nr) {
 		if (!ps->recursive ||
 		    !(ps->magic & PATHSPEC_MAXDEPTH) ||