diff --git a/libc/stdlib/strntoumax.c b/libc/stdlib/strntoumax.c
new file mode 100644
index 0000000..a151ef5
--- /dev/null
+++ b/libc/stdlib/strntoumax.c
@@ -0,0 +1,95 @@
+/*
+ * 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 <stddef.h>
+#include <stdint.h>
+#include <ctype.h>
+
+static inline int digitval(int ch)
+{
+    unsigned  d;
+
+    d = (unsigned)(ch - '0');
+    if (d < 10) return (int)d;
+
+    d = (unsigned)(ch - 'a');
+    if (d < 6) return (int)(d+10);
+
+    d = (unsigned)(ch - 'A');
+    if (d < 6) return (int)(d+10);
+
+    return -1;
+}
+
+uintmax_t
+strntoumax(const char *nptr, char **endptr, int base, size_t n)
+{
+    const unsigned char*  p   = nptr;
+    const unsigned char*  end = p + n;
+    int                   minus = 0;
+    uintmax_t             v = 0;
+    int                   d;
+
+    /* skip leading space */
+    while (p < end && isspace(*p))
+        p++;
+
+    /* Single optional + or - */
+    if (p < end) {
+        char c = p[0];
+        if ( c == '-' || c == '+' ) {
+            minus = (c == '-');
+            p++;
+        }
+    }
+
+    if ( base == 0 ) {
+        if ( p+2 < end && p[0] == '0' && (p[1] == 'x' || p[1] == 'X') ) {
+            p += 2;
+            base = 16;
+        } else if ( p+1 < end && p[0] == '0' ) {
+            p   += 1;
+            base = 8;
+        } else {
+            base = 10;
+        }
+    } else if ( base == 16 ) {
+        if ( p+2 < end && p[0] == '0' && (p[1] == 'x' || p[1] == 'X') ) {
+            p += 2;
+        }
+    }
+
+    while ( p < end && (d = digitval(*p)) >= 0 && d < base ) {
+        v = v*base + d;
+        p += 1;
+    }
+
+    if ( endptr )
+        *endptr = (char *)p;
+
+    return minus ? -v : v;
+}