diff --git a/cache.h b/cache.h
index bf468e5235..3f9ee86147 100644
--- a/cache.h
+++ b/cache.h
@@ -702,7 +702,11 @@ static inline unsigned int hexval(unsigned char c)
 #define DEFAULT_ABBREV 7
 
 extern int get_sha1(const char *str, unsigned char *sha1);
-extern int get_sha1_with_mode(const char *str, unsigned char *sha1, unsigned *mode);
+extern int get_sha1_with_mode_1(const char *str, unsigned char *sha1, unsigned *mode, int gently, const char *prefix);
+static inline int get_sha1_with_mode(const char *str, unsigned char *sha1, unsigned *mode)
+{
+	return get_sha1_with_mode_1(str, sha1, mode, 1, NULL);
+}
 extern int get_sha1_hex(const char *hex, unsigned char *sha1);
 extern char *sha1_to_hex(const unsigned char *sha1);	/* static buffer result! */
 extern int read_ref(const char *filename, unsigned char *sha1);
diff --git a/setup.c b/setup.c
index 2cf0f19937..3a07aa4df7 100644
--- a/setup.c
+++ b/setup.c
@@ -77,6 +77,18 @@ int check_filename(const char *prefix, const char *arg)
 	die_errno("failed to stat '%s'", arg);
 }
 
+static void NORETURN die_verify_filename(const char *prefix, const char *arg)
+{
+	unsigned char sha1[20];
+	unsigned mode;
+	/* try a detailed diagnostic ... */
+	get_sha1_with_mode_1(arg, sha1, &mode, 0, prefix);
+	/* ... or fall back the most general message. */
+	die("ambiguous argument '%s': unknown revision or path not in the working tree.\n"
+	    "Use '--' to separate paths from revisions", arg);
+
+}
+
 /*
  * Verify a filename that we got as an argument for a pathspec
  * entry. Note that a filename that begins with "-" never verifies
@@ -90,8 +102,7 @@ void verify_filename(const char *prefix, const char *arg)
 		die("bad flag '%s' used after filename", arg);
 	if (check_filename(prefix, arg))
 		return;
-	die("ambiguous argument '%s': unknown revision or path not in the working tree.\n"
-	    "Use '--' to separate paths from revisions", arg);
+	die_verify_filename(prefix, arg);
 }
 
 /*
diff --git a/sha1_name.c b/sha1_name.c
index 44bb62d270..ca8f9dba94 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -804,7 +804,96 @@ int get_sha1(const char *name, unsigned char *sha1)
 	return get_sha1_with_mode(name, sha1, &unused);
 }
 
-int get_sha1_with_mode(const char *name, unsigned char *sha1, unsigned *mode)
+/* Must be called only when object_name:filename doesn't exist. */
+static void diagnose_invalid_sha1_path(const char *prefix,
+				       const char *filename,
+				       const unsigned char *tree_sha1,
+				       const char *object_name)
+{
+	struct stat st;
+	unsigned char sha1[20];
+	unsigned mode;
+
+	if (!prefix)
+		prefix = "";
+
+	if (!lstat(filename, &st))
+		die("Path '%s' exists on disk, but not in '%s'.",
+		    filename, object_name);
+	if (errno == ENOENT || errno == ENOTDIR) {
+		char *fullname = xmalloc(strlen(filename)
+					     + strlen(prefix) + 1);
+		strcpy(fullname, prefix);
+		strcat(fullname, filename);
+
+		if (!get_tree_entry(tree_sha1, fullname,
+				    sha1, &mode)) {
+			die("Path '%s' exists, but not '%s'.\n"
+			    "Did you mean '%s:%s'?",
+			    fullname,
+			    filename,
+			    object_name,
+			    fullname);
+		}
+		die("Path '%s' does not exist in '%s'",
+		    filename, object_name);
+	}
+}
+
+/* Must be called only when :stage:filename doesn't exist. */
+static void diagnose_invalid_index_path(int stage,
+					const char *prefix,
+					const char *filename)
+{
+	struct stat st;
+	struct cache_entry *ce;
+	int pos;
+	unsigned namelen = strlen(filename);
+	unsigned fullnamelen;
+	char *fullname;
+
+	if (!prefix)
+		prefix = "";
+
+	/* Wrong stage number? */
+	pos = cache_name_pos(filename, namelen);
+	if (pos < 0)
+		pos = -pos - 1;
+	ce = active_cache[pos];
+	if (ce_namelen(ce) == namelen &&
+	    !memcmp(ce->name, filename, namelen))
+		die("Path '%s' is in the index, but not at stage %d.\n"
+		    "Did you mean ':%d:%s'?",
+		    filename, stage,
+		    ce_stage(ce), filename);
+
+	/* Confusion between relative and absolute filenames? */
+	fullnamelen = namelen + strlen(prefix);
+	fullname = xmalloc(fullnamelen + 1);
+	strcpy(fullname, prefix);
+	strcat(fullname, filename);
+	pos = cache_name_pos(fullname, fullnamelen);
+	if (pos < 0)
+		pos = -pos - 1;
+	ce = active_cache[pos];
+	if (ce_namelen(ce) == fullnamelen &&
+	    !memcmp(ce->name, fullname, fullnamelen))
+		die("Path '%s' is in the index, but not '%s'.\n"
+		    "Did you mean ':%d:%s'?",
+		    fullname, filename,
+		    ce_stage(ce), fullname);
+
+	if (!lstat(filename, &st))
+		die("Path '%s' exists on disk, but not in the index.", filename);
+	if (errno == ENOENT || errno == ENOTDIR)
+		die("Path '%s' does not exist (neither on disk nor in the index).",
+		    filename);
+
+	free(fullname);
+}
+
+
+int get_sha1_with_mode_1(const char *name, unsigned char *sha1, unsigned *mode, int gently, const char *prefix)
 {
 	int ret, bracket_depth;
 	int namelen = strlen(name);
@@ -850,6 +939,8 @@ int get_sha1_with_mode(const char *name, unsigned char *sha1, unsigned *mode)
 			}
 			pos++;
 		}
+		if (!gently)
+			diagnose_invalid_index_path(stage, prefix, cp);
 		return -1;
 	}
 	for (cp = name, bracket_depth = 0; *cp; cp++) {
@@ -862,9 +953,25 @@ int get_sha1_with_mode(const char *name, unsigned char *sha1, unsigned *mode)
 	}
 	if (*cp == ':') {
 		unsigned char tree_sha1[20];
-		if (!get_sha1_1(name, cp-name, tree_sha1))
-			return get_tree_entry(tree_sha1, cp+1, sha1,
-					      mode);
+		char *object_name = NULL;
+		if (!gently) {
+			object_name = xmalloc(cp-name+1);
+			strncpy(object_name, name, cp-name);
+			object_name[cp-name] = '\0';
+		}
+		if (!get_sha1_1(name, cp-name, tree_sha1)) {
+			const char *filename = cp+1;
+			ret = get_tree_entry(tree_sha1, filename, sha1, mode);
+			if (!gently) {
+				diagnose_invalid_sha1_path(prefix, filename,
+							   tree_sha1, object_name);
+				free(object_name);
+			}
+			return ret;
+		} else {
+			if (!gently)
+				die("Invalid object name '%s'.", object_name);
+		}
 	}
 	return ret;
 }
diff --git a/t/t1506-rev-parse-diagnosis.sh b/t/t1506-rev-parse-diagnosis.sh
new file mode 100755
index 0000000000..af721f9719
--- /dev/null
+++ b/t/t1506-rev-parse-diagnosis.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='test git rev-parse diagnosis for invalid argument'
+
+exec </dev/null
+
+. ./test-lib.sh
+
+HASH_file=
+
+test_expect_success 'set up basic repo' '
+	echo one > file.txt &&
+	mkdir subdir &&
+	echo two > subdir/file.txt &&
+	echo three > subdir/file2.txt &&
+	git add . &&
+	git commit -m init &&
+	echo four > index-only.txt &&
+	git add index-only.txt &&
+	echo five > disk-only.txt
+'
+
+test_expect_success 'correct file objects' '
+	HASH_file=$(git rev-parse HEAD:file.txt) &&
+	git rev-parse HEAD:subdir/file.txt &&
+	git rev-parse :index-only.txt &&
+	(cd subdir &&
+	 git rev-parse HEAD:subdir/file2.txt &&
+	 test $HASH_file = $(git rev-parse HEAD:file.txt) &&
+	 test $HASH_file = $(git rev-parse :file.txt) &&
+	 test $HASH_file = $(git rev-parse :0:file.txt) )
+'
+
+test_expect_success 'incorrect revision id' '
+	test_must_fail git rev-parse foobar:file.txt 2>error &&
+	grep "Invalid object name '"'"'foobar'"'"'." error &&
+	test_must_fail git rev-parse foobar 2> error &&
+	grep "unknown revision or path not in the working tree." error
+'
+
+test_expect_success 'incorrect file in sha1:path' '
+	test_must_fail git rev-parse HEAD:nothing.txt 2> error &&
+	grep "fatal: Path '"'"'nothing.txt'"'"' does not exist in '"'"'HEAD'"'"'" error &&
+	test_must_fail git rev-parse HEAD:index-only.txt 2> error &&
+	grep "fatal: Path '"'"'index-only.txt'"'"' exists on disk, but not in '"'"'HEAD'"'"'." error &&
+	(cd subdir &&
+	 test_must_fail git rev-parse HEAD:file2.txt 2> error &&
+	 grep "Did you mean '"'"'HEAD:subdir/file2.txt'"'"'?" error )
+'
+
+test_expect_success 'incorrect file in :path and :N:path' '
+	test_must_fail git rev-parse :nothing.txt 2> error &&
+	grep "fatal: Path '"'"'nothing.txt'"'"' does not exist (neither on disk nor in the index)." error &&
+	test_must_fail git rev-parse :1:nothing.txt 2> error &&
+	grep "Path '"'"'nothing.txt'"'"' does not exist (neither on disk nor in the index)." error &&
+	test_must_fail git rev-parse :1:file.txt 2> error &&
+	grep "Did you mean '"'"':0:file.txt'"'"'?" error &&
+	(cd subdir &&
+	 test_must_fail git rev-parse :1:file.txt 2> error &&
+	 grep "Did you mean '"'"':0:file.txt'"'"'?" error &&
+	 test_must_fail git rev-parse :file2.txt 2> error &&
+	 grep "Did you mean '"'"':0:subdir/file2.txt'"'"'?" error &&
+	 test_must_fail git rev-parse :2:file2.txt 2> error &&
+	 grep "Did you mean '"'"':0:subdir/file2.txt'"'"'?" error) &&
+	test_must_fail git rev-parse :disk-only.txt 2> error &&
+	grep "fatal: Path '"'"'disk-only.txt'"'"' exists on disk, but not in the index." error
+'
+
+test_done