diff --git a/CMakeLists.txt b/CMakeLists.txt
index e658976..060fd0b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -151,6 +151,8 @@ if(Threads_FOUND)
 endif(Threads_FOUND)
 if(ZLIB_FOUND)
   set(LIBVNCSERVER_HAVE_LIBZ 1)
+else()
+  unset(ZLIB_LIBRARIES) # would otherwise contain -NOTFOUND, confusing target_link_libraries()
 endif(ZLIB_FOUND)
 if(JPEG_FOUND)
   set(LIBVNCSERVER_HAVE_LIBJPEG 1)
@@ -158,8 +160,9 @@ endif(JPEG_FOUND)
 if(PNG_FOUND)
   set(LIBVNCSERVER_HAVE_LIBPNG 1)
 endif(PNG_FOUND)
-
-
+if(NOT OPENSSL_FOUND)
+    unset(OPENSSL_LIBRARIES) # would otherwise contain -NOTFOUND, confusing target_link_libraries()
+endif()
 if(SYSTEMD_FOUND)
   add_definitions(-DLIBVNCSERVER_WITH_SYSTEMD)
   include_directories(${SYSTEMD_INCLUDE_DIRS})