diff --git a/tests/qemu-iotests/049.out b/tests/qemu-iotests/049.out
index 8719c91b48..34e1b452e6 100644
--- a/tests/qemu-iotests/049.out
+++ b/tests/qemu-iotests/049.out
@@ -92,13 +92,10 @@ Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off comp
 == 3. Invalid sizes ==
 
 qemu-img create -f qcow2 TEST_DIR/t.qcow2 -- -1024
-qemu-img: Invalid image size specified. You may use k, M, G, T, P or E suffixes for
-qemu-img: kilobytes, megabytes, gigabytes, terabytes, petabytes and exabytes.
+qemu-img: Invalid image size specified. Must be between 0 and 9223372036854775807.
 
 qemu-img create -f qcow2 -o size=-1024 TEST_DIR/t.qcow2
-qemu-img: TEST_DIR/t.qcow2: Parameter 'size' expects a non-negative number below 2^64
-Optional suffix k, M, G, T, P or E means kilo-, mega-, giga-, tera-, peta-
-and exabytes, respectively.
+qemu-img: TEST_DIR/t.qcow2: Value '-1024' is out of range for parameter 'size'
 
 qemu-img create -f qcow2 TEST_DIR/t.qcow2 -- -1k
 qemu-img: Invalid image size specified. You may use k, M, G, T, P or E suffixes for
diff --git a/tests/qemu-iotests/178.out.qcow2 b/tests/qemu-iotests/178.out.qcow2
index 0d51fe401e..fe193fd5f4 100644
--- a/tests/qemu-iotests/178.out.qcow2
+++ b/tests/qemu-iotests/178.out.qcow2
@@ -13,8 +13,7 @@ qemu-img: Invalid option list: ,
 qemu-img: Invalid parameter 'snapshot.foo'
 qemu-img: Failed in parsing snapshot param 'snapshot.foo=bar'
 qemu-img: --output must be used with human or json as argument.
-qemu-img: Invalid image size specified. You may use k, M, G, T, P or E suffixes for
-qemu-img: kilobytes, megabytes, gigabytes, terabytes, petabytes and exabytes.
+qemu-img: Invalid image size specified. Must be between 0 and 9223372036854775807.
 qemu-img: Unknown file format 'foo'
 
 == Size calculation for a new file (human) ==
diff --git a/tests/qemu-iotests/178.out.raw b/tests/qemu-iotests/178.out.raw
index 116241ddef..445e460fad 100644
--- a/tests/qemu-iotests/178.out.raw
+++ b/tests/qemu-iotests/178.out.raw
@@ -13,8 +13,7 @@ qemu-img: Invalid option list: ,
 qemu-img: Invalid parameter 'snapshot.foo'
 qemu-img: Failed in parsing snapshot param 'snapshot.foo=bar'
 qemu-img: --output must be used with human or json as argument.
-qemu-img: Invalid image size specified. You may use k, M, G, T, P or E suffixes for
-qemu-img: kilobytes, megabytes, gigabytes, terabytes, petabytes and exabytes.
+qemu-img: Invalid image size specified. Must be between 0 and 9223372036854775807.
 qemu-img: Unknown file format 'foo'
 
 == Size calculation for a new file (human) ==
diff --git a/tests/unit/test-cutils.c b/tests/unit/test-cutils.c
index cfe1fc8a17..0e3215a46e 100644
--- a/tests/unit/test-cutils.c
+++ b/tests/unit/test-cutils.c
@@ -3519,10 +3519,9 @@ static void test_qemu_strtosz_trailing(void)
 static void test_qemu_strtosz_erange(void)
 {
     /* FIXME negative values fit better as ERANGE */
-    do_strtosz(" -0", -EINVAL /* FIXME -ERANGE */, 0, 0 /* FIXME 3 */);
-    do_strtosz("-1", -EINVAL /* FIXME -ERANGE */, 0, 0 /* FIXME 2 */);
-    do_strtosz_full("-2M", qemu_strtosz, -EINVAL /* FIXME -ERANGE */, 0,
-                    0 /* FIXME 2 */, -EINVAL, 0);
+    do_strtosz(" -0", -ERANGE, 0, 3);
+    do_strtosz("-1", -ERANGE, 0, 2);
+    do_strtosz_full("-2M", qemu_strtosz, -ERANGE, 0, 2, -EINVAL, 0);
     do_strtosz(" -.0", -EINVAL /* FIXME -ERANGE */, 0, 0 /* FIXME 4 */);
     do_strtosz_full("-.1k", qemu_strtosz, -EINVAL /* FIXME -ERANGE */, 0,
                     0 /* FIXME 3 */, -EINVAL, 0);
diff --git a/util/cutils.c b/util/cutils.c
index edfb71a217..e3a49209a9 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -201,6 +201,7 @@ static int64_t suffix_mul(char suffix, int64_t unit)
  * - hex with scaling suffix, such as 0x20M
  * - octal, such as 08
  * - fractional hex, such as 0x1.8
+ * - negative values, including -0
  * - floating point exponents, such as 1e3
  *
  * The end pointer will be returned in *end, if not NULL.  If there is
@@ -226,15 +227,10 @@ static int do_strtosz(const char *nptr, const char **end,
     int64_t mul;
 
     /* Parse integral portion as decimal. */
-    retval = qemu_strtou64(nptr, &endptr, 10, &val);
+    retval = parse_uint(nptr, &endptr, 10, &val);
     if (retval) {
         goto out;
     }
-    if (memchr(nptr, '-', endptr - nptr) != NULL) {
-        endptr = nptr;
-        retval = -EINVAL;
-        goto out;
-    }
     if (val == 0 && (*endptr == 'x' || *endptr == 'X')) {
         /* Input looks like hex; reparse, and insist on no fraction or suffix. */
         retval = qemu_strtou64(nptr, &endptr, 16, &val);