diff --git a/pkgs/applications/misc/calibre/default.nix b/pkgs/applications/misc/calibre/default.nix
index b3754fed17963..8f672deb693b5 100644
--- a/pkgs/applications/misc/calibre/default.nix
+++ b/pkgs/applications/misc/calibre/default.nix
@@ -104,7 +104,6 @@ mkDerivation rec {
       pillow
       pyqt-builder
       pyqt5
-      pyqtwebengine
       python
       regex
       sip
@@ -114,6 +113,11 @@ mkDerivation rec {
       pycryptodome
       # the following are distributed with calibre, but we use upstream instead
       odfpy
+    ] ++ lib.optionals (lib.lists.any (p: p == stdenv.hostPlatform.system) pyqtwebengine.meta.platforms) [
+      # much of calibre's functionality is usable without a web
+      # browser, so we enable building on platforms which qtwebengine
+      # does not support by simply omitting qtwebengine.
+      pyqtwebengine
     ] ++ lib.optional (unrarSupport) unrardll
   );
 
diff --git a/pkgs/applications/networking/browsers/qutebrowser/default.nix b/pkgs/applications/networking/browsers/qutebrowser/default.nix
index ecce98c9b46af..2e96266fd7372 100644
--- a/pkgs/applications/networking/browsers/qutebrowser/default.nix
+++ b/pkgs/applications/networking/browsers/qutebrowser/default.nix
@@ -132,5 +132,6 @@ in mkDerivationWith python3Packages.buildPythonApplication rec {
     description = "Keyboard-focused browser with a minimal GUI";
     license     = licenses.gpl3Plus;
     maintainers = with maintainers; [ jagajaga rnhmjoj ebzzry dotlambda ];
+    inherit (backendPackage.meta) platforms;
   };
 }
diff --git a/pkgs/development/libraries/qt-5/modules/qtwebengine.nix b/pkgs/development/libraries/qt-5/modules/qtwebengine.nix
index 3c5256908d882..ce087d49b5fae 100644
--- a/pkgs/development/libraries/qt-5/modules/qtwebengine.nix
+++ b/pkgs/development/libraries/qt-5/modules/qtwebengine.nix
@@ -240,7 +240,22 @@ qtModule {
   meta = with lib; {
     description = "A web engine based on the Chromium web browser";
     maintainers = with maintainers; [ matthewbauer ];
-    platforms = platforms.unix;
+
+    # qtwebengine-5.15.8: "QtWebEngine can only be built for x86,
+    # x86-64, ARM, Aarch64, and MIPSel architectures."
+    platforms =
+      lib.trivial.pipe lib.systems.doubles.all [
+        (map (double: lib.systems.elaborate { system = double; }))
+        (lib.lists.filter (parsedPlatform: with parsedPlatform;
+          isUnix &&
+          (isx86_32  ||
+           isx86_64  ||
+           isAarch32 ||
+           isAarch64 ||
+           (isMips && isLittleEndian))))
+        (map (plat: plat.system))
+      ];
+
     # This build takes a long time; particularly on slow architectures
     timeout = 24 * 3600;
     # we are still stuck with MacOS SDK 10.12 on x86_64-darwin
diff --git a/pkgs/development/python-modules/pyqtwebengine/default.nix b/pkgs/development/python-modules/pyqtwebengine/default.nix
index f59694876cc49..12021e52271b3 100644
--- a/pkgs/development/python-modules/pyqtwebengine/default.nix
+++ b/pkgs/development/python-modules/pyqtwebengine/default.nix
@@ -66,6 +66,6 @@ in buildPythonPackage rec {
     description = "Python bindings for Qt5";
     homepage    = "http://www.riverbankcomputing.co.uk";
     license     = licenses.gpl3;
-    platforms   = platforms.mesaPlatforms;
+    platforms   = lib.lists.intersectLists qtwebengine.meta.platforms platforms.mesaPlatforms;
   };
 }