diff --git a/libc/Android.bp b/libc/Android.bp
index b278774..e259eba 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -567,6 +567,7 @@
     srcs: [
         "stdio/vfprintf.cpp",
         "stdio/vfwprintf.cpp",
+        "upstream-openbsd/lib/libc/string/memmem.c",
         "upstream-openbsd/lib/libc/string/strstr.c",
     ],
     cflags: [
@@ -1075,7 +1076,6 @@
         "bionic/mblen.cpp",
         "bionic/mbrtoc16.cpp",
         "bionic/mbrtoc32.cpp",
-        "bionic/memmem.cpp",
         "bionic/mempcpy.cpp",
         "bionic/mkdir.cpp",
         "bionic/mkfifo.cpp",
diff --git a/libc/NOTICE b/libc/NOTICE
index 7f2e8b0..0a5f226 100644
--- a/libc/NOTICE
+++ b/libc/NOTICE
@@ -4267,6 +4267,29 @@
 
 -------------------------------------------------------------------
 
+Copyright (c) 2005-2020 Rich Felker, et al.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+-------------------------------------------------------------------
+
 Copyright (c) 2007 David Schultz
 All rights reserved.
 
diff --git a/libc/bionic/memmem.cpp b/libc/bionic/memmem.cpp
deleted file mode 100644
index 019e772..0000000
--- a/libc/bionic/memmem.cpp
+++ /dev/null
@@ -1,60 +0,0 @@
-/*
- * Copyright (C) 2008 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <string.h>
-
-void* memmem(const void* void_haystack, size_t n, const void* void_needle, size_t m) {
-  const unsigned char* haystack = reinterpret_cast<const unsigned char*>(void_haystack);
-  const unsigned char* needle = reinterpret_cast<const unsigned char*>(void_needle);
-
-  if (n < m) return nullptr;
-
-  if (m == 0) return const_cast<void*>(void_haystack);
-  if (m == 1) return const_cast<void*>(memchr(haystack, needle[0], n));
-
-  // This uses the "Not So Naive" algorithm, a very simple but usually effective algorithm.
-  // http://www-igm.univ-mlv.fr/~lecroq/string/
-  const unsigned char* y = haystack;
-  const unsigned char* x = needle;
-  size_t j = 0;
-  size_t k = 1, l = 2;
-
-  if (x[0] == x[1]) {
-    k = 2;
-    l = 1;
-  }
-  while (j <= n-m) {
-    if (x[1] != y[j+1]) {
-      j += k;
-    } else {
-      if (!memcmp(x+2, y+j+2, m-2) && x[0] == y[j]) return const_cast<unsigned char*>(&y[j]);
-      j += l;
-    }
-  }
-  return nullptr;
-}
diff --git a/libc/upstream-openbsd/lib/libc/string/memmem.c b/libc/upstream-openbsd/lib/libc/string/memmem.c
new file mode 100644
index 0000000..3b180b4
--- /dev/null
+++ b/libc/upstream-openbsd/lib/libc/string/memmem.c
@@ -0,0 +1,184 @@
+/*	$OpenBSD: memmem.c,v 1.5 2020/04/16 12:39:28 claudio Exp $ */
+
+/*
+ * Copyright (c) 2005-2020 Rich Felker, et al.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <string.h>
+#include <stdint.h>
+
+static char *
+twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+	uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
+	for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
+		if (hw == nw) return (char *)h-2;
+	return hw == nw ? (char *)h-2 : 0;
+}
+
+static char *
+threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
+	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
+	for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
+		if (hw == nw) return (char *)h-3;
+	return hw == nw ? (char *)h-3 : 0;
+}
+
+static char *
+fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
+	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+	for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
+		if (hw == nw) return (char *)h-4;
+	return hw == nw ? (char *)h-4 : 0;
+}
+
+#define MAX(a,b) ((a)>(b)?(a):(b))
+#define MIN(a,b) ((a)<(b)?(a):(b))
+
+#define BITOP(a,b,op) \
+ ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
+
+/*
+ * Maxime Crochemore and Dominique Perrin, Two-way string-matching,
+ * Journal of the ACM, 38(3):651-675, July 1991.
+ */
+static char *
+twoway_memmem(const unsigned char *h, const unsigned char *z,
+    const unsigned char *n, size_t l)
+{
+	size_t i, ip, jp, k, p, ms, p0, mem, mem0;
+	size_t byteset[32 / sizeof(size_t)] = { 0 };
+	size_t shift[256];
+
+	/* Computing length of needle and fill shift table */
+	for (i=0; i<l; i++)
+		BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
+
+	/* Compute maximal suffix */
+	ip = -1; jp = 0; k = p = 1;
+	while (jp+k<l) {
+		if (n[ip+k] == n[jp+k]) {
+			if (k == p) {
+				jp += p;
+				k = 1;
+			} else k++;
+		} else if (n[ip+k] > n[jp+k]) {
+			jp += k;
+			k = 1;
+			p = jp - ip;
+		} else {
+			ip = jp++;
+			k = p = 1;
+		}
+	}
+	ms = ip;
+	p0 = p;
+
+	/* And with the opposite comparison */
+	ip = -1; jp = 0; k = p = 1;
+	while (jp+k<l) {
+		if (n[ip+k] == n[jp+k]) {
+			if (k == p) {
+				jp += p;
+				k = 1;
+			} else k++;
+		} else if (n[ip+k] < n[jp+k]) {
+			jp += k;
+			k = 1;
+			p = jp - ip;
+		} else {
+			ip = jp++;
+			k = p = 1;
+		}
+	}
+	if (ip+1 > ms+1) ms = ip;
+	else p = p0;
+
+	/* Periodic needle? */
+	if (memcmp(n, n+p, ms+1)) {
+		mem0 = 0;
+		p = MAX(ms, l-ms-1) + 1;
+	} else mem0 = l-p;
+	mem = 0;
+
+	/* Search loop */
+	for (;;) {
+		/* If remainder of haystack is shorter than needle, done */
+		if (z-h < l) return 0;
+
+		/* Check last byte first; advance by shift on mismatch */
+		if (BITOP(byteset, h[l-1], &)) {
+			k = l-shift[h[l-1]];
+			if (k) {
+				if (k < mem) k = mem;
+				h += k;
+				mem = 0;
+				continue;
+			}
+		} else {
+			h += l;
+			mem = 0;
+			continue;
+		}
+
+		/* Compare right half */
+		for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
+		if (k < l) {
+			h += k-ms;
+			mem = 0;
+			continue;
+		}
+		/* Compare left half */
+		for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
+		if (k <= mem) return (char *)h;
+		h += p;
+		mem = mem0;
+	}
+}
+
+void *
+memmem(const void *h0, size_t k, const void *n0, size_t l)
+{
+	const unsigned char *h = h0, *n = n0;
+
+	/* Return immediately on empty needle */
+	if (!l) return (void *)h;
+
+	/* Return immediately when needle is longer than haystack */
+	if (k<l) return 0;
+
+	/* Use faster algorithms for short needles */
+	h = memchr(h0, *n, k);
+	if (!h || l==1) return (void *)h;
+	k -= h - (const unsigned char *)h0;
+	if (k<l) return 0;
+	if (l==2) return twobyte_memmem(h, k, n);
+	if (l==3) return threebyte_memmem(h, k, n);
+	if (l==4) return fourbyte_memmem(h, k, n);
+
+	return twoway_memmem(h, h+k, n, l);
+}
+DEF_WEAK(memmem);
diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index 0ed0598..f157416 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -1538,13 +1538,31 @@
 }
 
 TEST(STRING_TEST, memmem_smoke) {
-  const char haystack[] = "big\0daddy\0giant\0haystacks";
-  ASSERT_EQ(haystack, memmem(haystack, sizeof(haystack), "", 0));
-  ASSERT_EQ(haystack + 3, memmem(haystack, sizeof(haystack), "", 1));
+  const char haystack[] = "big\0daddy/giant\0haystacks!";
+
+  // The current memmem() implementation has special cases for needles of
+  // lengths 0, 1, 2, 3, and 4, plus a long needle case. We test matches at the
+  // beginning, middle, and end of the haystack.
+
+  ASSERT_EQ(haystack + 0, memmem(haystack, sizeof(haystack), "", 0));
+
   ASSERT_EQ(haystack + 0, memmem(haystack, sizeof(haystack), "b", 1));
-  ASSERT_EQ(haystack + 1, memmem(haystack, sizeof(haystack), "i", 1));
-  ASSERT_EQ(haystack + 4, memmem(haystack, sizeof(haystack), "da", 2));
-  ASSERT_EQ(haystack + 8, memmem(haystack, sizeof(haystack), "y\0g", 3));
+  ASSERT_EQ(haystack + 0, memmem(haystack, sizeof(haystack), "bi", 2));
+  ASSERT_EQ(haystack + 0, memmem(haystack, sizeof(haystack), "big", 3));
+  ASSERT_EQ(haystack + 0, memmem(haystack, sizeof(haystack), "big\0", 4));
+  ASSERT_EQ(haystack + 0, memmem(haystack, sizeof(haystack), "big\0d", 5));
+
+  ASSERT_EQ(haystack + 2, memmem(haystack, sizeof(haystack), "g", 1));
+  ASSERT_EQ(haystack + 10, memmem(haystack, sizeof(haystack), "gi", 2));
+  ASSERT_EQ(haystack + 10, memmem(haystack, sizeof(haystack), "gia", 3));
+  ASSERT_EQ(haystack + 10, memmem(haystack, sizeof(haystack), "gian", 4));
+  ASSERT_EQ(haystack + 10, memmem(haystack, sizeof(haystack), "giant", 5));
+
+  ASSERT_EQ(haystack + 25, memmem(haystack, sizeof(haystack), "!", 1));
+  ASSERT_EQ(haystack + 24, memmem(haystack, sizeof(haystack), "s!", 2));
+  ASSERT_EQ(haystack + 23, memmem(haystack, sizeof(haystack), "ks!", 3));
+  ASSERT_EQ(haystack + 22, memmem(haystack, sizeof(haystack), "cks!", 4));
+  ASSERT_EQ(haystack + 21, memmem(haystack, sizeof(haystack), "acks!", 5));
 }
 
 TEST(STRING_TEST, strstr_smoke) {