Index: lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -7728,16 +7728,43 @@
 INTERCEPTOR(long long, strtonum, const char *nptr, long long minval,
             long long maxval, const char **errstr) {
   void *ctx;
+  INTMAX_T res;
+  int saved_errno;
   COMMON_INTERCEPTOR_ENTER(ctx, strtonum, nptr, minval, maxval, errstr);
-  if (nptr)
-    COMMON_INTERCEPTOR_READ_RANGE(ctx, nptr, REAL(strlen)(nptr) + 1);
-  long long ret = REAL(strtonum)(nptr, minval, maxval, errstr);
-  if (errstr) {
-    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, errstr, sizeof(const char *));
-    if (*errstr)
-      COMMON_INTERCEPTOR_WRITE_RANGE(ctx, *errstr, REAL(strlen)(*errstr) + 1);
+  const char *rerrstr;
+  if (!errstr)
+    errstr = &rerrstr;
+
+  if (minval > maxval) {
+    *errstr = "invalid";
+    goto skip;
   }
-  return ret;
+
+  saved_errno = errno;
+  errno = 0;
+
+  char *real_endptr;
+  res = REAL(strtoimax)(nptr, &real_endptr, 10);
+  StrtolFixAndCheck(ctx, nptr, nullptr, real_endptr, 10);
+  if (nptr == real_endptr || *real_endptr != '\0')
+    *errstr = "invalid";
+  else if ((res == INTMAX_MAX && errno == errno_ERANGE) || (maxval < res))
+    *errstr = "too large";
+  else if ((res == INTMAX_MIN && errno == errno_ERANGE) || (minval > res))
+    *errstr = "too small";
+  else
+    *errstr = nullptr;
+
+  errno = saved_errno;
+
+ skip:
+  COMMON_INTERCEPTOR_WRITE_RANGE(ctx, errstr, sizeof(*errstr));
+  if (*errstr) {
+    res = 0;
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, *errstr, REAL(strlen)(*errstr) + 1);
+  }
+
+  return res;
 }
 #define INIT_STRTONUM COMMON_INTERCEPT_FUNCTION(strtonum)
 #else
Index: lib/sanitizer_common/sanitizer_errno_codes.h
===================================================================
--- lib/sanitizer_common/sanitizer_errno_codes.h
+++ lib/sanitizer_common/sanitizer_errno_codes.h
@@ -25,6 +25,7 @@
 #define errno_ENOMEM 12
 #define errno_EBUSY 16
 #define errno_EINVAL 22
+#define errno_ERANGE 34
 
 // Those might not present or their value differ on different platforms.
 extern const int errno_EOWNERDEAD;
Index: lib/sanitizer_common/sanitizer_internal_defs.h
===================================================================
--- lib/sanitizer_common/sanitizer_internal_defs.h
+++ lib/sanitizer_common/sanitizer_internal_defs.h
@@ -363,6 +363,10 @@
 #define INT64_MAX              (__INT64_C(9223372036854775807))
 #undef UINT64_MAX
 #define UINT64_MAX             (__UINT64_C(18446744073709551615))
+#undef INTMAX_MIN
+#define INTMAX_MIN             INT64_MIN
+#undef INTMAX_MAX
+#define INTMAX_MAX             INT64_MAX
 #undef UINTPTR_MAX
 #if SANITIZER_WORDSIZE == 64
 # define UINTPTR_MAX           (18446744073709551615UL)
Index: test/sanitizer_common/TestCases/NetBSD/strtonum.cc
===================================================================
--- /dev/null
+++ test/sanitizer_common/TestCases/NetBSD/strtonum.cc
@@ -0,0 +1,58 @@
+// RUN: %clangxx -O0 -g %s -o %t && %run %t 2>&1 | FileCheck %s
+
+#define _OPENBSD_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(void) {
+  const char *errstr;
+
+  printf("strtonum\n");
+
+  long long l = strtonum("100", 1, 100, &errstr);
+  if (errstr)
+    abort();
+  printf("%lld\n", l);
+
+  l = strtonum("200", 1, 100, &errstr);
+  if (!errstr)
+    abort();
+  printf("%s\n", errstr);
+
+  l = strtonum("300", 1000, 1001, &errstr);
+  if (!errstr)
+    abort();
+  printf("%s\n", errstr);
+
+  l = strtonum("abc", 1000, 1001, &errstr);
+  if (!errstr)
+    abort();
+  printf("%s\n", errstr);
+
+  l = strtonum("1000", 1001, 1000, &errstr);
+  if (!errstr)
+    abort();
+  printf("%s\n", errstr);
+
+  l = strtonum("1000abc", 1000, 1001, &errstr);
+  if (!errstr)
+    abort();
+  printf("%s\n", errstr);
+
+  l = strtonum("1000.0", 1000, 1001, &errstr);
+  if (!errstr)
+    abort();
+  printf("%s\n", errstr);
+
+  // CHECK: strtonum
+  // CHECK: 100
+  // CHECK: too large
+  // CHECK: too small
+  // CHECK: invalid
+  // CHECK: invalid
+  // CHECK: invalid
+  // CHECK: invalid
+
+  return 0;
+}