diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
index 0a7b324a8f..d9b9b95f16 100644
--- a/include/libvirt/libvirt.h.in
+++ b/include/libvirt/libvirt.h.in
@@ -2415,7 +2415,7 @@ typedef enum {
 } virStorageVolResizeFlags;
 
 int                     virStorageVolResize             (virStorageVolPtr vol,
-                                                         long long capacity,
+                                                         unsigned long long capacity,
                                                          unsigned int flags);
 
 
diff --git a/src/driver.h b/src/driver.h
index ba7dbc49b3..2e2042e3b7 100644
--- a/src/driver.h
+++ b/src/driver.h
@@ -1277,7 +1277,7 @@ typedef int
                                unsigned int flags);
 typedef int
         (*virDrvStorageVolResize) (virStorageVolPtr vol,
-                                   long long capacity,
+                                   unsigned long long capacity,
                                    unsigned int flags);
 
 typedef int
diff --git a/src/libvirt.c b/src/libvirt.c
index e702a3421b..c609202e4e 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -13014,16 +13014,20 @@ error:
  * Normally, this operation should only be used to enlarge capacity;
  * but if @flags contains VIR_STORAGE_RESIZE_SHRINK, it is possible to
  * attempt a reduction in capacity even though it might cause data loss.
+ * If VIR_STORAGE_RESIZE_DELTA is also present, then @capacity is
+ * subtracted from the current size; without it, @capacity represents
+ * the absolute new size regardless of whether it is larger or smaller
+ * than the current size.
  *
  * Returns 0 on success, or -1 on error.
  */
 int
 virStorageVolResize(virStorageVolPtr vol,
-                    long long capacity,
+                    unsigned long long capacity,
                     unsigned int flags)
 {
     virConnectPtr conn;
-    VIR_DEBUG("vol=%p capacity=%lld flags=%x", vol, capacity, flags);
+    VIR_DEBUG("vol=%p capacity=%llu flags=%x", vol, capacity, flags);
 
     virResetLastError();
 
@@ -13040,12 +13044,9 @@ virStorageVolResize(virStorageVolPtr vol,
        goto error;
     }
 
-    /* Negative capacity is valid only with both delta and shrink;
-     * zero capacity is valid with either delta or shrink.  */
-    if ((capacity < 0 && !(flags & VIR_STORAGE_VOL_RESIZE_DELTA) &&
-         !(flags & VIR_STORAGE_VOL_RESIZE_SHRINK)) ||
-        (capacity == 0 && !((flags & VIR_STORAGE_VOL_RESIZE_DELTA) ||
-                            (flags & VIR_STORAGE_VOL_RESIZE_SHRINK)))) {
+    /* Zero capacity is only valid with either delta or shrink.  */
+    if (capacity == 0 && !((flags & VIR_STORAGE_VOL_RESIZE_DELTA) ||
+                           (flags & VIR_STORAGE_VOL_RESIZE_SHRINK))) {
         virLibStorageVolError(VIR_ERR_INVALID_ARG, __FUNCTION__);
         goto error;
     }
diff --git a/src/remote/remote_protocol.x b/src/remote/remote_protocol.x
index b58925a235..b2c84261af 100644
--- a/src/remote/remote_protocol.x
+++ b/src/remote/remote_protocol.x
@@ -1709,7 +1709,7 @@ struct remote_storage_vol_get_path_ret {
 
 struct remote_storage_vol_resize_args {
     remote_nonnull_storage_vol vol;
-    hyper capacity;
+    unsigned hyper capacity;
     unsigned int flags;
 };
 
diff --git a/src/remote_protocol-structs b/src/remote_protocol-structs
index 5eac9bf9f0..e9137a90b9 100644
--- a/src/remote_protocol-structs
+++ b/src/remote_protocol-structs
@@ -1282,7 +1282,7 @@ struct remote_storage_vol_get_path_ret {
 };
 struct remote_storage_vol_resize_args {
         remote_nonnull_storage_vol vol;
-        int64_t                    capacity;
+        uint64_t                   capacity;
         u_int                      flags;
 };
 struct remote_node_num_of_devices_args {