https://bugs.gentoo.org/880407

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -288,7 +288,6 @@ add_subdirectory(common/libftoa)
 add_subdirectory(${EXTERNAL_LIBRARIES}/UTF)
 add_subdirectory(common/libBuffer)
 add_subdirectory(${EXTERNAL_LIBRARIES}/MathMLSolver)
-add_subdirectory(${EXTERNAL_LIBRARIES}/zlib)
 
 # building OpenCOLLADA libs
 add_subdirectory(COLLADABaseUtils)
--- a/DAEValidator/CMakeLists.txt
+++ b/DAEValidator/CMakeLists.txt
@@ -80,11 +80,8 @@ if (NOT LIBXML2_FOUND)
 else ()
     list(APPEND Libraries ${LIBXML2_LIBRARIES})
 endif ()
-if (USE_STATIC)
-        list(APPEND Libraries zlib_static)
-    else ()
-        list(APPEND Libraries zlib_shared)
-    endif ()
+find_package(ZLIB REQUIRED)
+list(APPEND Libraries ZLIB::ZLIB)
 if (WIN32)
 	list(APPEND Libraries ws2_32.lib)
 endif ()
@@ -208,10 +205,3 @@ else ()
     include_directories(${LIBXML2_INCLUDE_DIR})
 endif ()
 
-# zlib
-if (USE_STATIC)
-	add_dependencies(DAEValidatorExecutable zlib_static)
-else ()
-	add_dependencies(DAEValidatorExecutable zlib_shared)
-endif ()
-include_directories("../Externals/zlib/include")