--- a/toolkit/components/telemetry/TelemetryEnvironment.jsm
+++ b/toolkit/components/telemetry/TelemetryEnvironment.jsm
@@ -1308,20 +1308,20 @@ EnvironmentCache.prototype = {
       data.kernelVersion = forceToStringOrNull(getSysinfoProperty("kernel_version", null));
     } else if (AppConstants.platform === "win") {
       // The path to the "UBR" key, queried to get additional version details on Windows.
       const WINDOWS_UBR_KEY_PATH = "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion";
 
       let versionInfo = getWindowsVersionInfo();
       data.servicePackMajor = versionInfo.servicePackMajor;
       data.servicePackMinor = versionInfo.servicePackMinor;
-      // We only need the build number and UBR if we're at or above Windows 10.
+      data.windowsBuildNumber = versionInfo.buildNumber;
+      // We only need the UBR if we're at or above Windows 10.
       if (typeof(data.version) === "string" &&
           Services.vc.compare(data.version, "10") >= 0) {
-        data.windowsBuildNumber = versionInfo.buildNumber;
         // Query the UBR key and only add it to the environment if it's available.
         // |readRegKey| doesn't throw, but rather returns 'undefined' on error.
         let ubr = WindowsRegistry.readRegKey(Ci.nsIWindowsRegKey.ROOT_KEY_LOCAL_MACHINE,
                                              WINDOWS_UBR_KEY_PATH, "UBR",
                                              Ci.nsIWindowsRegKey.WOW64_64);
         data.windowsUBR = (ubr !== undefined) ? ubr : null;
       }
       data.installYear = getSysinfoProperty("installYear", null);

--- a/toolkit/components/telemetry/docs/data/environment.rst
+++ b/toolkit/components/telemetry/docs/data/environment.rst
@@ -112,17 +112,17 @@ Structure:
           isTablet: <bool>, // null on failure
         },
         os: {
             name: <string>, // "Windows_NT" or null on failure
             version: <string>, // e.g. "6.1", null on failure
             kernelVersion: <string>, // android/b2g only or null on failure
             servicePackMajor: <number>, // windows only or null on failure
             servicePackMinor: <number>, // windows only or null on failure
-            windowsBuildNumber: <number>, // windows 10 only or null on failure
+            windowsBuildNumber: <number>, // windows only or null on failure
             windowsUBR: <number>, // windows 10 only or null on failure
             installYear: <number>, // windows only or null on failure
             locale: <string>, // "en" or null on failure
         },
         hdd: {
           profile: { // hdd where the profile folder is located
               model: <string>, // windows only or null on failure
               revision: <string>, // windows only or null on failure
@@ -357,17 +357,17 @@ os
 
 This object contains operating system information.
 
 - ``name``: the name of the OS.
 - ``version``: a string representing the OS version.
 - ``kernelVersion``: an Android/B2G only string representing the kernel version.
 - ``servicePackMajor``: the Windows only major version number for the installed service pack.
 - ``servicePackMinor``: the Windows only minor version number for the installed service pack.
-- ``windowsBuildNumber``: the Windows build number, only available for Windows >= 10.
+- ``windowsBuildNumber``: the Windows build number.
 - ``windowsUBR``: the Windows UBR number, only available for Windows >= 10. This value is incremented by Windows cumulative updates patches.
 - ``installYear``: the Windows only integer representing the year the OS was installed.
 - ``locale``: the string representing the OS locale.
 
 addons
 ------
 
 activeAddons