diff --git a/lib/gui/app/models/store.js b/lib/gui/app/models/store.js
index f005f263..341df642 100644
--- a/lib/gui/app/models/store.js
+++ b/lib/gui/app/models/store.js
@@ -56,8 +56,6 @@ const verifyNoNilFields = (object, fields, name) => {
  * @private
  */
 const flashStateNoNilFields = [
-  'percentage',
-  'eta',
   'speed',
   'totalSpeed'
 ]
@@ -94,8 +92,8 @@ const DEFAULT_STATE = Immutable.fromJS({
     successful: 0,
     failed: 0,
     percentage: 0,
-    speed: 0,
-    totalSpeed: 0
+    speed: null,
+    totalSpeed: null
   }
 })
 
@@ -255,18 +253,6 @@ const storeReducer = (state = DEFAULT_STATE, action) => {
         })
       }
 
-      if (!utils.isValidPercentage(action.data.percentage)) {
-        throw errors.createError({
-          title: `Invalid state percentage: ${action.data.percentage}`
-        })
-      }
-
-      if (!_.isNumber(action.data.eta)) {
-        throw errors.createError({
-          title: `Invalid state eta: ${action.data.eta}`
-        })
-      }
-
       return state.set('flashState', Immutable.fromJS(action.data))
     }
 
diff --git a/lib/gui/app/modules/progress-status.js b/lib/gui/app/modules/progress-status.js
index 57d60536..6e2dae99 100644
--- a/lib/gui/app/modules/progress-status.js
+++ b/lib/gui/app/modules/progress-status.js
@@ -18,6 +18,7 @@
 
 const settings = require('../models/settings')
 const utils = require('../../../shared/utils')
+const units = require('../../../shared/units')
 
 /**
  * @summary Make the progress status subtitle string
@@ -58,7 +59,11 @@ exports.fromFlashState = (state) => {
 
     return 'Finishing...'
   } else if (isFlashing) {
-    return `${state.percentage}% Flashing`
+    if (state.percentage != null) {
+      return `${state.percentage}% Flashing`
+    } else {
+      return `${units.bytesToClosestUnit(state.position)} flashed`
+    }
   } else if (isValidating) {
     return `${state.percentage}% Validating`
   } else if (!isFlashing && !isValidating) {
diff --git a/lib/gui/app/os/window-progress.js b/lib/gui/app/os/window-progress.js
index dcc8bccf..0053cc69 100644
--- a/lib/gui/app/os/window-progress.js
+++ b/lib/gui/app/os/window-progress.js
@@ -90,7 +90,9 @@ exports.currentWindow = electron.remote.getCurrentWindow()
  * })
  */
 exports.set = (state) => {
-  exports.currentWindow.setProgressBar(utils.percentageToFloat(state.percentage))
+  if (state.percentage != null) {
+    exports.currentWindow.setProgressBar(utils.percentageToFloat(state.percentage))
+  }
   exports.currentWindow.setTitle(getWindowTitle(state))
 }
 
diff --git a/lib/gui/app/pages/main/templates/main.tpl.html b/lib/gui/app/pages/main/templates/main.tpl.html
index 684f8a60..dd181600 100644
--- a/lib/gui/app/pages/main/templates/main.tpl.html
+++ b/lib/gui/app/pages/main/templates/main.tpl.html
@@ -133,9 +133,9 @@
           <span class="glyphicon glyphicon-remove-sign"></span>
         </button>
 
-        <p class="step-footer step-footer-split" ng-if="main.state.getFlashState().speed && main.state.getFlashState().percentage != 100">
+        <p class="step-footer step-footer-split" ng-if="main.state.getFlashState().speed != null && main.state.getFlashState().percentage != 100">
           <span ng-bind="main.state.getFlashState().speed.toFixed(2) + ' MB/s'"></span>
-          <span>ETA: {{ main.state.getFlashState().eta | secondsToDate | amDateFormat:'m[m]ss[s]' }}</span>
+          <span ng-if="main.state.getFlashState().eta != null">ETA: {{ main.state.getFlashState().eta | secondsToDate | amDateFormat:'m[m]ss[s]' }}</span>
         </p>
 
         <div class="target-status-wrap" ng-if="main.state.getFlashState().failed">
diff --git a/lib/gui/modules/child-writer.js b/lib/gui/modules/child-writer.js
index c358d729..a4599cad 100644
--- a/lib/gui/modules/child-writer.js
+++ b/lib/gui/modules/child-writer.js
@@ -108,15 +108,17 @@ function pipeRegularSourceToDestination(source, destination, verify, onProgress,
     flashing: destination.destinations.length,
     verifying: 0,
     failed: 0,
-    successful: 0
+    successful: 0,
+    type: step
   }
   function updateState() {
+    state.type = step
     state.failed = errors.size
     state.active = destination.destinations.length - state.failed
     if (step === 'flashing') {
       state.flashing = state.active
       state.verifying = 0
-    } else if (step === 'verifying') {
+    } else if (step === 'check') {
       state.flashing = 0
       state.verifying = state.active
     } else if (step === 'finished') {
@@ -128,7 +130,7 @@ function pipeRegularSourceToDestination(source, destination, verify, onProgress,
     progressEvent.percentage = progressEvent.position / sourceMetadata.size * 100
     // NOTE: We need to guard against this becoming Infinity,
     // because that value isn't transmitted properly over IPC and becomes `null`
-    progressEvent.eta = progressEvent.speed ? (sourceMetadata.size - progressEvent.position) / progressEvent.speed : 0
+    progressEvent.eta = progressEvent.speed ? (sourceMetadata.size - progressEvent.position) / progressEvent.speed : null
     progressEvent.totalSpeed = progressEvent.speed * state.active
     Object.assign(progressEvent, state)
     onProgress(progressEvent)
@@ -166,8 +168,13 @@ function pipeRegularSourceToDestination(source, destination, verify, onProgress,
     })
   })
   .then(() => {
+    if (sourceMetadata.size == null) {
+      // This is needed for compressed sources for which we don't know the uncompressed size:
+      // After writing the image, we know the size.
+      sourceMetadata.size = lastPosition
+    }
     if (verify) {
-      step = 'verifying'
+      step = 'check'
       updateState()
       const verifier = destination.createVerifier(checksum, sourceMetadata.size)
       verifier.on('progress', onProgress2)
diff --git a/lib/shared/units.js b/lib/shared/units.js
index 16b00293..6e4f5741 100644
--- a/lib/shared/units.js
+++ b/lib/shared/units.js
@@ -29,7 +29,7 @@ const prettyBytes = require('pretty-bytes')
  * @description
  * 1 MB = 1e+6 B
  */
-const MEGABYTE_TO_BYTE_RATIO = 1e+6
+const MEGABYTE_TO_BYTE_RATIO = 1000000
 
 /**
  * @summary Milliseconds in a day