diff --git a/.gitignore b/.gitignore
index 5bfb234591..9ec40fa9fb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -199,6 +199,7 @@
 /test-revision-walking
 /test-run-command
 /test-sha1
+/test-sha1-array
 /test-sigchain
 /test-string-list
 /test-subprocess
diff --git a/Makefile b/Makefile
index f34a2d4cb8..356feb5c86 100644
--- a/Makefile
+++ b/Makefile
@@ -568,6 +568,7 @@ TEST_PROGRAMS_NEED_X += test-revision-walking
 TEST_PROGRAMS_NEED_X += test-run-command
 TEST_PROGRAMS_NEED_X += test-scrap-cache-tree
 TEST_PROGRAMS_NEED_X += test-sha1
+TEST_PROGRAMS_NEED_X += test-sha1-array
 TEST_PROGRAMS_NEED_X += test-sigchain
 TEST_PROGRAMS_NEED_X += test-string-list
 TEST_PROGRAMS_NEED_X += test-subprocess
diff --git a/sha1-lookup.c b/sha1-lookup.c
index 2dd851598a..5f069214d9 100644
--- a/sha1-lookup.c
+++ b/sha1-lookup.c
@@ -84,8 +84,6 @@ int sha1_pos(const unsigned char *sha1, void *table, size_t nr,
 				die("BUG: assertion failed in binary search");
 			}
 		}
-		if (18 <= ofs)
-			die("cannot happen -- lo and hi are identical");
 	}
 
 	do {
diff --git a/t/t0064-sha1-array.sh b/t/t0064-sha1-array.sh
new file mode 100755
index 0000000000..50b31ffe75
--- /dev/null
+++ b/t/t0064-sha1-array.sh
@@ -0,0 +1,94 @@
+#!/bin/sh
+
+test_description='basic tests for the SHA1 array implementation'
+. ./test-lib.sh
+
+echo20 () {
+	prefix="${1:+$1 }"
+	shift
+	while test $# -gt 0
+	do
+		echo "$prefix$1$1$1$1$1$1$1$1$1$1$1$1$1$1$1$1$1$1$1$1"
+		shift
+	done
+}
+
+test_expect_success 'ordered enumeration' '
+	echo20 "" 44 55 88 aa >expect &&
+	{
+		echo20 append 88 44 aa 55 &&
+		echo for_each_unique
+	} | test-sha1-array >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'ordered enumeration with duplicate suppression' '
+	echo20 "" 44 55 88 aa >expect &&
+	{
+		echo20 append 88 44 aa 55 &&
+		echo20 append 88 44 aa 55 &&
+		echo for_each_unique
+	} | test-sha1-array >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'lookup' '
+	{
+		echo20 append 88 44 aa 55 &&
+		echo20 lookup 55
+	} | test-sha1-array >actual &&
+	n=$(cat actual) &&
+	test "$n" -eq 1
+'
+
+test_expect_success 'lookup non-existing entry' '
+	{
+		echo20 append 88 44 aa 55 &&
+		echo20 lookup 33
+	} | test-sha1-array >actual &&
+	n=$(cat actual) &&
+	test "$n" -lt 0
+'
+
+test_expect_success 'lookup with duplicates' '
+	{
+		echo20 append 88 44 aa 55 &&
+		echo20 append 88 44 aa 55 &&
+		echo20 lookup 55
+	} | test-sha1-array >actual &&
+	n=$(cat actual) &&
+	test "$n" -ge 2 &&
+	test "$n" -le 3
+'
+
+test_expect_success 'lookup non-existing entry with duplicates' '
+	{
+		echo20 append 88 44 aa 55 &&
+		echo20 append 88 44 aa 55 &&
+		echo20 lookup 66
+	} | test-sha1-array >actual &&
+	n=$(cat actual) &&
+	test "$n" -lt 0
+'
+
+test_expect_success 'lookup with almost duplicate values' '
+	{
+		echo "append 5555555555555555555555555555555555555555" &&
+		echo "append 555555555555555555555555555555555555555f" &&
+		echo20 lookup 55
+	} | test-sha1-array >actual &&
+	n=$(cat actual) &&
+	test "$n" -eq 0
+'
+
+test_expect_success 'lookup with single duplicate value' '
+	{
+		echo20 append 55 55 &&
+		echo20 lookup 55
+	} | test-sha1-array >actual &&
+	n=$(cat actual) &&
+	test "$n" -ge 0 &&
+	test "$n" -le 1
+'
+
+test_done
diff --git a/test-sha1-array.c b/test-sha1-array.c
new file mode 100644
index 0000000000..ddc491eff9
--- /dev/null
+++ b/test-sha1-array.c
@@ -0,0 +1,34 @@
+#include "cache.h"
+#include "sha1-array.h"
+
+static void print_sha1(const unsigned char sha1[20], void *data)
+{
+	puts(sha1_to_hex(sha1));
+}
+
+int main(int argc, char **argv)
+{
+	struct sha1_array array = SHA1_ARRAY_INIT;
+	struct strbuf line = STRBUF_INIT;
+
+	while (strbuf_getline(&line, stdin, '\n') != EOF) {
+		const char *arg;
+		unsigned char sha1[20];
+
+		if (skip_prefix(line.buf, "append ", &arg)) {
+			if (get_sha1_hex(arg, sha1))
+				die("not a hexadecimal SHA1: %s", arg);
+			sha1_array_append(&array, sha1);
+		} else if (skip_prefix(line.buf, "lookup ", &arg)) {
+			if (get_sha1_hex(arg, sha1))
+				die("not a hexadecimal SHA1: %s", arg);
+			printf("%d\n", sha1_array_lookup(&array, sha1));
+		} else if (!strcmp(line.buf, "clear"))
+			sha1_array_clear(&array);
+		else if (!strcmp(line.buf, "for_each_unique"))
+			sha1_array_for_each_unique(&array, print_sha1, NULL);
+		else
+			die("unknown command: %s", line.buf);
+	}
+	return 0;
+}