diff --git a/content/base/public/nsContentUtils.h b/content/base/public/nsContentUtils.h
index e932022af1e..e25713060fd 100644
--- a/content/base/public/nsContentUtils.h
+++ b/content/base/public/nsContentUtils.h
@@ -1570,6 +1570,13 @@ public:
                                       uint32_t aDisplayWidth,
                                       uint32_t aDisplayHeight);
 
+  /**
+   * Constrain the viewport calculations from the GetViewportInfo() function
+   * in order to always return sane minimum/maximum values. This modifies the
+   * ViewportInfo struct passed as an input parameter, in place.
+   */
+  static void ConstrainViewportValues(ViewportInfo& aViewInfo);
+
   /**
    * The device-pixel-to-CSS-px ratio used to adjust meta viewport values.
    */
diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index f716ce84c38..14a51d9df09 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -250,8 +250,8 @@ namespace {
 /**
  * Default values for the ViewportInfo structure.
  */
-static const float    kViewportMinScale = 0.0;
-static const float    kViewportMaxScale = 10.0;
+static const double   kViewportMinScale = 0.0;
+static const double   kViewportMaxScale = 10.0;
 static const uint32_t kViewportMinWidth = 200;
 static const uint32_t kViewportMaxWidth = 10000;
 static const uint32_t kViewportMinHeight = 223;
@@ -5101,6 +5101,29 @@ static void ProcessViewportToken(nsIDocument *aDocument,
 #define IS_SEPARATOR(c) ((c == '=') || (c == ',') || (c == ';') || \
                          (c == '\t') || (c == '\n') || (c == '\r'))
 
+/* static */
+void
+nsContentUtils::ConstrainViewportValues(ViewportInfo& aViewInfo)
+{
+  aViewInfo.maxZoom = NS_MIN(aViewInfo.maxZoom, kViewportMaxScale);
+  aViewInfo.maxZoom = NS_MAX(aViewInfo.maxZoom, kViewportMinScale);
+  aViewInfo.minZoom = NS_MIN(aViewInfo.minZoom, kViewportMaxScale);
+  aViewInfo.minZoom = NS_MAX(aViewInfo.minZoom, kViewportMinScale);
+
+  // Constrain the min/max zoom as specified at:
+  // dev.w3.org/csswg/css-device-adapt section 6.2
+  aViewInfo.maxZoom = NS_MAX(aViewInfo.minZoom, aViewInfo.maxZoom);
+
+  aViewInfo.defaultZoom = NS_MIN(aViewInfo.defaultZoom, aViewInfo.maxZoom);
+  aViewInfo.defaultZoom = NS_MAX(aViewInfo.defaultZoom, aViewInfo.minZoom);
+
+  aViewInfo.width = NS_MIN(aViewInfo.width, kViewportMaxWidth);
+  aViewInfo.width = NS_MAX(aViewInfo.width, kViewportMinWidth);
+
+  aViewInfo.height = NS_MIN(aViewInfo.height, kViewportMaxHeight);
+  aViewInfo.height = NS_MAX(aViewInfo.height, kViewportMinHeight);
+}
+
 /* static */
 ViewportInfo
 nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
@@ -5111,6 +5134,10 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
   ret.defaultZoom = 1.0;
   ret.autoSize = true;
   ret.allowZoom = true;
+  ret.width = aDisplayWidth;
+  ret.height = aDisplayHeight;
+  ret.minZoom = kViewportMinScale;
+  ret.maxZoom = kViewportMaxScale;
 
   nsAutoString viewport;
   aDocument->GetHeaderData(nsGkAtoms::viewport, viewport);
@@ -5128,6 +5155,7 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
             (docId.Find("Mobile") != -1) ||
             (docId.Find("WML") != -1))
         {
+          nsContentUtils::ConstrainViewportValues(ret);
           return ret;
         }
       }
@@ -5136,6 +5164,7 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
     nsAutoString handheldFriendly;
     aDocument->GetHeaderData(nsGkAtoms::handheldFriendly, handheldFriendly);
     if (handheldFriendly.EqualsLiteral("true")) {
+      nsContentUtils::ConstrainViewportValues(ret);
       return ret;
     }
   }
@@ -5150,9 +5179,6 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
     scaleMinFloat = kViewportMinScale;
   }
 
-  scaleMinFloat = NS_MIN(scaleMinFloat, kViewportMaxScale);
-  scaleMinFloat = NS_MAX(scaleMinFloat, kViewportMinScale);
-
   nsAutoString maxScaleStr;
   aDocument->GetHeaderData(nsGkAtoms::viewport_maximum_scale, maxScaleStr);
 
@@ -5165,16 +5191,11 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
     scaleMaxFloat = kViewportMaxScale;
   }
 
-  scaleMaxFloat = NS_MIN(scaleMaxFloat, kViewportMaxScale);
-  scaleMaxFloat = NS_MAX(scaleMaxFloat, kViewportMinScale);
-
   nsAutoString scaleStr;
   aDocument->GetHeaderData(nsGkAtoms::viewport_initial_scale, scaleStr);
 
   nsresult scaleErrorCode;
   float scaleFloat = scaleStr.ToFloat(&scaleErrorCode);
-  scaleFloat = NS_MIN(scaleFloat, scaleMaxFloat);
-  scaleFloat = NS_MAX(scaleFloat, scaleMinFloat);
 
   nsAutoString widthStr, heightStr;
 
@@ -5235,18 +5256,12 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
     }
   }
 
-  width = NS_MIN(width, kViewportMaxWidth);
-  width = NS_MAX(width, kViewportMinWidth);
-
   // Also recalculate the default zoom, if it wasn't specified in the metadata,
   // and the width is specified.
   if (scaleStr.IsEmpty() && !widthStr.IsEmpty()) {
     scaleFloat = NS_MAX(scaleFloat, float(aDisplayWidth) / float(width));
   }
 
-  height = NS_MIN(height, kViewportMaxHeight);
-  height = NS_MAX(height, kViewportMinHeight);
-
   // We need to perform a conversion, but only if the initial or maximum
   // scale were set explicitly by the user.
   if (!scaleStr.IsEmpty() && NS_SUCCEEDED(scaleErrorCode)) {
@@ -5274,6 +5289,8 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
   ret.minZoom = scaleMinFloat;
   ret.maxZoom = scaleMaxFloat;
   ret.autoSize = autoSize;
+
+  nsContentUtils::ConstrainViewportValues(ret);
   return ret;
 }
 
diff --git a/content/test/reftest/bug798068-ref.xhtml b/content/test/reftest/bug798068-ref.xhtml
new file mode 100644
index 00000000000..2ddcd4a0218
--- /dev/null
+++ b/content/test/reftest/bug798068-ref.xhtml
@@ -0,0 +1,19 @@
+<?xml version = '1.0' encoding = 'utf-8'?>
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <script>
+      function doTest() {
+        var Ci = Components.interfaces;
+        var defaultZoom = {}, allowZoom = {}, minZoom = {}, maxZoom ={}, width = {}, height = {}, autoSize = {};
+        var windowUtils = window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+        windowUtils.getViewportInfo(1, 1, defaultZoom, allowZoom, minZoom, maxZoom, width, height, autoSize);
+        document.getElementById("minZoom").innerHTML = minZoom.value.toPrecision(10);
+        document.getElementById("maxZoom").innerHTML = maxZoom.value.toPrecision(10);
+      }
+    </script>
+  </head>
+  <body onload="doTest();">
+  MinZoom: <span id="minZoom"></span><br />
+  MaxZoom: <span id="maxZoom"></span>
+  </body>
+</html>
diff --git a/content/test/reftest/bug798068.xhtml b/content/test/reftest/bug798068.xhtml
new file mode 100644
index 00000000000..6e2a6a35787
--- /dev/null
+++ b/content/test/reftest/bug798068.xhtml
@@ -0,0 +1,20 @@
+<?xml version = '1.0' encoding = 'utf-8'?>
+<!DOCTYPE html PUBLIC "-//WAPFORUM//DTD XHTML Mobile 1.0//EN" "http://www.wapforum.org/DTD/xhtml-mobile10.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <script>
+      function doTest() {
+        var Ci = Components.interfaces;
+        var defaultZoom = {}, allowZoom = {}, minZoom = {}, maxZoom ={}, width = {}, height = {}, autoSize = {};
+        var windowUtils = window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+        windowUtils.getViewportInfo(1, 1, defaultZoom, allowZoom, minZoom, maxZoom, width, height, autoSize);
+        document.getElementById("minZoom").innerHTML = minZoom.value.toPrecision(10);
+        document.getElementById("maxZoom").innerHTML = maxZoom.value.toPrecision(10);
+      }
+    </script>
+  </head>
+  <body onload="doTest();">
+  MinZoom: <span id="minZoom"></span><br />
+  MaxZoom: <span id="maxZoom"></span>
+  </body>
+</html>
diff --git a/content/test/reftest/reftest.list b/content/test/reftest/reftest.list
index 206e8c876d6..1a299de9088 100644
--- a/content/test/reftest/reftest.list
+++ b/content/test/reftest/reftest.list
@@ -15,3 +15,4 @@ skip-if(xulFennec) include ../../canvas/test/reftest/reftest.list
 == bug592366-2.html bug592366-ref.html
 == bug592366-1.xhtml bug592366-ref.xhtml
 == bug592366-2.xhtml bug592366-ref.xhtml
+== bug798068.xhtml bug798068-ref.xhtml