diff --git a/builder/openstack/run_config.go b/builder/openstack/run_config.go
index 56fccb4f3..5a2efd023 100644
--- a/builder/openstack/run_config.go
+++ b/builder/openstack/run_config.go
@@ -40,6 +40,7 @@ type RunConfig struct {
 	UseBlockStorageVolume  bool   `mapstructure:"use_blockstorage_volume"`
 	VolumeName             string `mapstructure:"volume_name"`
 	VolumeType             string `mapstructure:"volume_type"`
+	VolumeSize             int    `mapstructure:"volume_size"`
 	VolumeAvailabilityZone string `mapstructure:"volume_availability_zone"`
 
 	// Not really used, but here for BC
diff --git a/builder/openstack/step_create_volume.go b/builder/openstack/step_create_volume.go
index 28b01c0b4..ec1734a06 100644
--- a/builder/openstack/step_create_volume.go
+++ b/builder/openstack/step_create_volume.go
@@ -35,20 +35,25 @@ func (s *StepCreateVolume) Run(_ context.Context, state multistep.StateBag) mult
 		state.Put("error", err)
 		return multistep.ActionHalt
 	}
-	imageClient, err := config.imageV2Client()
-	if err != nil {
-		err = fmt.Errorf("Error initializing image client: %s", err)
-		state.Put("error", err)
-		return multistep.ActionHalt
-	}
+
+	volumeSize := config.VolumeSize
 
 	// Get needed volume size from the source image.
-	volumeSize, err := GetVolumeSize(imageClient, sourceImage)
-	if err != nil {
-		err := fmt.Errorf("Error creating volume: %s", err)
-		state.Put("error", err)
-		ui.Error(err.Error())
-		return multistep.ActionHalt
+	if volumeSize == 0 {
+		imageClient, err := config.imageV2Client()
+		if err != nil {
+			err = fmt.Errorf("Error initializing image client: %s", err)
+			state.Put("error", err)
+			return multistep.ActionHalt
+		}
+
+		volumeSize, err = GetVolumeSize(imageClient, sourceImage)
+		if err != nil {
+			err := fmt.Errorf("Error creating volume: %s", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
 	}
 
 	ui.Say("Creating volume...")
diff --git a/website/source/docs/builders/openstack.html.md b/website/source/docs/builders/openstack.html.md
index 263610c0f..3320f7ea2 100644
--- a/website/source/docs/builders/openstack.html.md
+++ b/website/source/docs/builders/openstack.html.md
@@ -275,6 +275,11 @@ builder.
     isn't specified, the default enforced by your OpenStack cluster will be
     used.
 
+-   `volume_size` (int) - Size of the Block Storage service volume in GB. If this
+    isn't specified, it is set to source image min disk value (if set) or
+    calculated from the source image bytes size. Note that in some cases this
+    needs to be specified, if `use_blockstorage_volume` is true.
+
 -   `volume_availability_zone` (string) - Availability zone of the Block
     Storage service volume. If omitted, Compute instance availability zone will
     be used. If both of Compute instance and Block Storage volume availability