diff --git a/changes/bug5786_range b/changes/bug5786_range
new file mode 100644
index 0000000000..40ac4d2467
--- /dev/null
+++ b/changes/bug5786_range
@@ -0,0 +1,8 @@
+  o Minor bugfixes:
+    - Make our number-parsing functions always treat too-large values
+      as an error, even when those values exceed the width of the
+      underlying type. Previously, if the caller provided these
+      functions with minima or maxima set to the extreme values of the
+      underlying integer type, these functions would return those
+      values on overflow rather than treating overflow as an error.
+      Fix for part of bug 5786; bugfix on Tor 0.0.9.
\ No newline at end of file
diff --git a/src/common/util.c b/src/common/util.c
index 276c6dd13b..30bf6879ac 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -870,6 +870,9 @@ tor_digest256_is_zero(const char *digest)
 /* Helper: common code to check whether the result of a strtol or strtoul or
  * strtoll is correct. */
 #define CHECK_STRTOX_RESULT()                           \
+  /* Did an overflow occur? */                          \
+  if (errno == ERANGE)                                  \
+    goto err;                                           \
   /* Was at least one character converted? */           \
   if (endptr == s)                                      \
     goto err;                                           \
@@ -911,6 +914,8 @@ tor_parse_long(const char *s, int base, long min, long max,
       *ok = 0;
     return 0;
   }
+
+  errno = 0;
   r = strtol(s, &endptr, base);
   CHECK_STRTOX_RESULT();
 }
@@ -928,6 +933,8 @@ tor_parse_ulong(const char *s, int base, unsigned long min,
       *ok = 0;
     return 0;
   }
+
+  errno = 0;
   r = strtoul(s, &endptr, base);
   CHECK_STRTOX_RESULT();
 }
@@ -939,6 +946,7 @@ tor_parse_double(const char *s, double min, double max, int *ok, char **next)
   char *endptr;
   double r;
 
+  errno = 0;
   r = strtod(s, &endptr);
   CHECK_STRTOX_RESULT();
 }
@@ -958,6 +966,7 @@ tor_parse_uint64(const char *s, int base, uint64_t min,
     return 0;
   }
 
+  errno = 0;
 #ifdef HAVE_STRTOULL
   r = (uint64_t)strtoull(s, &endptr, base);
 #elif defined(_WIN32)
diff --git a/src/test/test_util.c b/src/test/test_util.c
index 7a455e06a9..e8f043a2c5 100644
--- a/src/test/test_util.c
+++ b/src/test/test_util.c
@@ -755,6 +755,21 @@ test_util_strmisc(void)
   test_eq(-10.0, d);
   }
 
+  {
+    /* Test tor_parse_* where we overflow/underflow the underlying type. */
+    /* This string should overflow 64-bit ints. */
+#define TOOBIG "100000000000000000000000000"
+    test_eq(0L, tor_parse_long(TOOBIG, 10, LONG_MIN, LONG_MAX, &i, NULL));
+    test_eq(i, 0);
+    test_eq(0L, tor_parse_long("-"TOOBIG, 10, LONG_MIN, LONG_MAX, &i, NULL));
+    test_eq(i, 0);
+    test_eq(0UL, tor_parse_ulong(TOOBIG, 10, 0, ULONG_MAX, &i, NULL));
+    test_eq(i, 0);
+    test_eq(U64_LITERAL(0), tor_parse_uint64(TOOBIG, 10,
+                                             0, UINT64_MAX, &i, NULL));
+    test_eq(i, 0);
+  }
+
   /* Test snprintf */
   /* Returning -1 when there's not enough room in the output buffer */
   test_eq(-1, tor_snprintf(buf, 0, "Foo"));