diff --git a/src/gui/components/result-panel/result-panel.tsx b/src/gui/components/result-panel/result-panel.tsx
index bd09639..be3e3bb 100644
--- a/src/gui/components/result-panel/result-panel.tsx
+++ b/src/gui/components/result-panel/result-panel.tsx
@@ -13,6 +13,8 @@ import MathUtil from '../../solver/math-util'
 import CoordinatesUtil, { ImageCoordinateFrame } from '../../solver/coordinates-util'
 import Button from '../common/button'
 import Checkbox from '../settings-panel/checkbox'
+import Solver from '../../solver/solver'
+import strings from '../../strings/strings'
 
 interface ResultPanelProps {
   globalSettings: GlobalSettings
@@ -273,6 +275,12 @@ export default class ResultPanel extends React.PureComponent<ResultPanelProps> {
     }
 
     const displayFocalLength = this.props.resultDisplaySettings.displayAbsoluteFocalLength
+    const proportionsMatch = Solver.imageProportionsMatchSensor(
+      cameraParameters.imageWidth,
+      cameraParameters.imageHeight,
+      sensorWidth,
+      sensorHeight
+    )
 
     return (
       <div className='panel-section bottom-border'>
@@ -282,6 +290,12 @@ export default class ResultPanel extends React.PureComponent<ResultPanelProps> {
           onChange={ (enabled: boolean) => { this.props.onDisplayAbsoluteFocalLengthChanged(enabled) } }
         />
         { displayFocalLength ? this.renderCameraPresetForm(absoluteFocalLength, cameraData) : null }
+        { !proportionsMatch ? (<BulletList
+          messages={
+            [ strings.imageSensorProportionsMismatch ]
+          }
+          type={BulletListType.Warnings}
+        />) : null }
       </div>
     )
   }
diff --git a/src/gui/solver/solver.ts b/src/gui/solver/solver.ts
index b14784a..e5642bc 100644
--- a/src/gui/solver/solver.ts
+++ b/src/gui/solver/solver.ts
@@ -9,6 +9,7 @@ import CoordinatesUtil, { ImageCoordinateFrame } from './coordinates-util'
 import { SolverResult, CameraParameters } from './solver-result'
 import { defaultSolverResult } from './../defaults/solver-result'
 import { cameraPresets } from './camera-presets'
+import strings from '../strings/strings'
 
 /**
  * The solver handles estimation of focal length and camera orientation
@@ -68,8 +69,8 @@ export default class Solver {
       relativeFocalLength = 2 * absoluteFocalLength / sensorHeight
     }
 
-    if (Math.abs(sensorAspectRatio - imageWidth / imageHeight) > 0.01) { // TODO: choose epsilon
-      result.warnings.push('Image/sensor aspect ratio mismatch')
+    if (!this.imageProportionsMatchSensor(sensorWidth, sensorHeight, imageWidth, imageHeight)) {
+      result.warnings.push(strings.imageSensorProportionsMismatch)
     }
 
     // Compute the input vanishing point in image plane coordinates
@@ -246,6 +247,23 @@ export default class Solver {
     return result
   }
 
+  static imageProportionsMatchSensor(imageWidth: number, imageHeight: number, sensorWidth: number, sensorHeight: number): boolean {
+    if (sensorHeight == 0 || sensorWidth == 0 || imageWidth == 0 || imageHeight == 0) {
+      return false
+    }
+    const epsilon = 0.01
+    const imageAspectRatio = imageWidth / imageHeight
+    const sensorAspectRatio = sensorWidth / sensorHeight
+
+    const imageFitsSensor = Math.abs(sensorAspectRatio - imageAspectRatio) < epsilon
+    const rotated90DegImageFitsSensor = Math.abs(sensorAspectRatio - 1 / imageAspectRatio) < epsilon
+    if (!imageFitsSensor && !rotated90DegImageFitsSensor) {
+      return false
+    }
+
+    return true
+  }
+
   /**
    * Computes the focal length based on two vanishing points and a center of projection.
    * See 3.2 "Determining the focal length from a single image"
diff --git a/src/gui/strings/strings.ts b/src/gui/strings/strings.ts
index 2bd1136..e8488ee 100644
--- a/src/gui/strings/strings.ts
+++ b/src/gui/strings/strings.ts
@@ -1,6 +1,7 @@
 const strings = {
   customCameraPresetName: 'Custom camera',
-  unitMm: 'mm'
+  unitMm: 'mm',
+  imageSensorProportionsMismatch: 'Image/sensor proportions mismatch'
 }
 
 export default strings