diff --git a/docs/formatstorage.html.in b/docs/formatstorage.html.in
index acb21faa81..d0e4319c50 100644
--- a/docs/formatstorage.html.in
+++ b/docs/formatstorage.html.in
@@ -236,13 +236,22 @@
         <br/>
         By default this is specified in bytes, but an optional attribute
         <code>unit</code> can be specified to adjust the passed value.
-        Values can be: 'K' (kibibytes, 2<sup>10</sup> or 1024 bytes),
-        'M' (mebibytes, 2<sup>20</sup> or 1,048,576 bytes), 'G'
-        (gibibytes, 2<sup>30</sup> or 1,073,741,824 bytes), 'T'
-        (tebibytes, 2<sup>40</sup> or 1,099,511,627,776 bytes), 'P'
-        (pebibytes, 2<sup>50</sup> or 1,125,899,906,842,624 bytes), or
-        'E' (exbibytes, 2<sup>60</sup> or 1,152,921,504,606,846,976
-        bytes).  <span class="since">Since 0.4.1</span></dd>
+        Values can be: 'B' or 'bytes' for bytes, 'KB' (kilobytes,
+        10<sup>3</sup> or 1000 bytes), 'K' or 'KiB' (kibibytes,
+        2<sup>10</sup> or 1024 bytes), 'MB' (megabytes, 10<sup>6</sup>
+        or 1,000,000 bytes), 'M' or 'MiB' (mebibytes, 2<sup>20</sup>
+        or 1,048,576 bytes), 'GB' (gigabytes, 10<sup>9</sup> or
+        1,000,000,000 bytes), 'G' or 'GiB' (gibibytes, 2<sup>30</sup>
+        or 1,073,741,824 bytes), 'TB' (terabytes, 10<sup>12</sup> or
+        1,000,000,000,000 bytes), 'T' or 'TiB' (tebibytes,
+        2<sup>40</sup> or 1,099,511,627,776 bytes), 'PB' (petabytes,
+        10<sup>15</sup> or 1,000,000,000,000,000 bytes), 'P' or 'PiB'
+        (pebibytes, 2<sup>50</sup> or 1,125,899,906,842,624 bytes),
+        'EB' (exabytes, 10<sup>18</sup> or 1,000,000,000,000,000,000
+        bytes), or 'E' or 'EiB' (exbibytes, 2<sup>60</sup> or
+        1,152,921,504,606,846,976 bytes).  <span class="since">Since
+        0.4.1, multi-character <code>unit</code> since
+        0.9.11</span></dd>
       <dt><code>capacity</code></dt>
       <dd>Providing the logical capacity for the volume. This value is
         in bytes by default, but a <code>unit</code> attribute can be
diff --git a/docs/schemas/basictypes.rng b/docs/schemas/basictypes.rng
index a50349c602..cc0bc1286d 100644
--- a/docs/schemas/basictypes.rng
+++ b/docs/schemas/basictypes.rng
@@ -140,7 +140,7 @@
 
   <define name='unit'>
     <data type='string'>
-      <param name='pattern'>(bytes)|[kKmMgGtTpPeE]</param>
+      <param name='pattern'>([bB]([yY][tT][eE][sS]?)?)|([kKmMgGtTpPeE]([iI]?[bB])?)</param>
     </data>
   </define>
   <define name='scaledInteger'>
diff --git a/src/conf/storage_conf.c b/src/conf/storage_conf.c
index 07f3f5b6dc..bdf62184c4 100644
--- a/src/conf/storage_conf.c
+++ b/src/conf/storage_conf.c
@@ -944,64 +944,17 @@ virStoragePoolDefFormat(virStoragePoolDefPtr def) {
 static int
 virStorageSize(const char *unit,
                const char *val,
-               unsigned long long *ret) {
-    unsigned long long mult;
-    char *end;
-
-    if (!unit) {
-        mult = 1;
-    } else {
-        switch (unit[0]) {
-        case 'k':
-        case 'K':
-            mult = 1024ull;
-            break;
-
-        case 'm':
-        case 'M':
-            mult = 1024ull * 1024ull;
-            break;
-
-        case 'g':
-        case 'G':
-            mult = 1024ull * 1024ull * 1024ull;
-            break;
-
-        case 't':
-        case 'T':
-            mult = 1024ull * 1024ull * 1024ull * 1024ull;
-            break;
-
-        case 'p':
-        case 'P':
-            mult = 1024ull * 1024ull * 1024ull * 1024ull * 1024ull;
-            break;
-
-        case 'e':
-        case 'E':
-            mult = 1024ull * 1024ull * 1024ull * 1024ull * 1024ull *
-                1024ull;
-            break;
-
-        default:
-            virStorageReportError(VIR_ERR_XML_ERROR,
-                                  _("unknown size units '%s'"), unit);
-            return -1;
-        }
-    }
-
-    if (virStrToLong_ull (val, &end, 10, ret) < 0) {
+               unsigned long long *ret)
+{
+    if (virStrToLong_ull(val, NULL, 10, ret) < 0) {
         virStorageReportError(VIR_ERR_XML_ERROR,
                               "%s", _("malformed capacity element"));
         return -1;
     }
-    if (*ret > (ULLONG_MAX / mult)) {
-        virStorageReportError(VIR_ERR_XML_ERROR,
-                              "%s", _("capacity element value too large"));
-            return -1;
-    }
-
-    *ret *= mult;
+    /* off_t is signed, so you cannot create a file larger than 2**63
+     * bytes in the first place.  */
+    if (virScaleInteger(ret, unit, 1, LLONG_MAX) < 0)
+        return -1;
 
     return 0;
 }
diff --git a/tests/storagevolxml2xmlin/vol-file-backing.xml b/tests/storagevolxml2xmlin/vol-file-backing.xml
index c1a5837c6a..d23349e658 100644
--- a/tests/storagevolxml2xmlin/vol-file-backing.xml
+++ b/tests/storagevolxml2xmlin/vol-file-backing.xml
@@ -1,8 +1,8 @@
 <volume>
   <name>sparse.img</name>
   <source/>
-  <capacity>10000000000</capacity>
-  <allocation>0</allocation>
+  <capacity unit='GB'>10</capacity>
+  <allocation unit='MiB'>0</allocation>
   <target>
     <path>/var/lib/libvirt/images/sparse.img</path>
     <permissions>
diff --git a/tests/storagevolxml2xmlin/vol-file.xml b/tests/storagevolxml2xmlin/vol-file.xml
index d7de0aa23c..fdca510101 100644
--- a/tests/storagevolxml2xmlin/vol-file.xml
+++ b/tests/storagevolxml2xmlin/vol-file.xml
@@ -1,8 +1,8 @@
 <volume>
   <name>sparse.img</name>
   <source/>
-  <capacity unit="T">1</capacity>
-  <allocation>0</allocation>
+  <capacity unit="TiB">1</capacity>
+  <allocation unit="bytes">0</allocation>
   <target>
     <path>/var/lib/libvirt/images/sparse.img</path>
     <permissions>