diff --git a/classes/cmake-extra-sanity.bbclass b/classes/cmake-extra-sanity.bbclass
new file mode 100644
index 00000000..b00bbb68
--- /dev/null
+++ b/classes/cmake-extra-sanity.bbclass
@@ -0,0 +1,9 @@
+do_install_append() {
+    # avoid strange prefixing seen often
+    old_dir=`pwd`
+    cd ${D}
+    if grep -qr 'usr\/\/usr' ; then
+        bbfatal 'usr//usr found in ${PN} - check sources for PREFIX or better CMAKE_INSTALL_PREFIX!'
+    fi
+    cd $old_dir
+}
diff --git a/classes/kde-base.bbclass b/classes/kde-base.bbclass
index 9e44b843..79fb2edb 100644
--- a/classes/kde-base.bbclass
+++ b/classes/kde-base.bbclass
@@ -6,7 +6,7 @@ KDE_BRANCH ?= "master"
 SRC_URI = "git://anongit.kde.org/${BPN};protocol=git;branch=${KDE_BRANCH}"
 
 # extra-cmake-modules cause dependent to check for python
-inherit cmake_qt5 pythonnative
+inherit cmake_qt5 cmake-extra-sanity pythonnative
 
 FILES_${PN} += "${libdir}/plugins/kf5 ${datadir}/kf5"
 FILES_${PN}-dev += "${libdir}/cmake"