diff --git a/CMakeExternals/ExternalProjectList.cmake b/CMakeExternals/ExternalProjectList.cmake
index d47c03b93a..9873030a41 100644
--- a/CMakeExternals/ExternalProjectList.cmake
+++ b/CMakeExternals/ExternalProjectList.cmake
@@ -1,44 +1,44 @@
 mitkFunctionAddExternalProject(NAME Poco        ON  COMPONENTS Foundation Net Util XML Zip)
 mitkFunctionAddExternalProject(NAME DCMTK       ON  DOC "EXPERIMENTAL, superbuild only: Use DCMTK in MITK")
 mitkFunctionAddExternalProject(NAME OpenIGTLink OFF)
 
 mitkFunctionAddExternalProject(NAME tinyxml     ON  ADVANCED)
 mitkFunctionAddExternalProject(NAME GDCM        ON  ADVANCED)
 mitkFunctionAddExternalProject(NAME GLUT        OFF ADVANCED)
 mitkFunctionAddExternalProject(NAME Raptor2     OFF ADVANCED)
 mitkFunctionAddExternalProject(NAME Eigen       ON  ADVANCED DOC "Use the Eigen library")
 mitkFunctionAddExternalProject(NAME ANN         ON  ADVANCED DOC "Use Approximate Nearest Neighbor Library")
 mitkFunctionAddExternalProject(NAME CppUnit     ON  ADVANCED DOC "Use CppUnit for unit tests")
 
 mitkFunctionAddExternalProject(NAME PCRE        OFF ADVANCED NO_PACKAGE)
 
 mitkFunctionAddExternalProject(NAME HDF5        ON ADVANCED)
 mitkFunctionAddExternalProject(NAME BetData     OFF ADVANCED)
 mitkFunctionAddExternalProject(NAME OpenMP      ON)
 
 # -----------------------------------------
 # The following external projects must be
 # ordered according to their
 # inter-dependencies
 
 mitkFunctionAddExternalProject(NAME SWIG      OFF ADVANCED NO_PACKAGE DEPENDS PCRE)
 mitkFunctionAddExternalProject(NAME Python    OFF)
 mitkFunctionAddExternalProject(NAME OpenCV    OFF)
 mitkFunctionAddExternalProject(NAME Vigra     OFF          DEPENDS HDF5)
 
 # These are "hard" dependencies and always set to ON
 mitkFunctionAddExternalProject(NAME ITK       ON           NO_CACHE DEPENDS HDF5)
 mitkFunctionAddExternalProject(NAME VTK       ON           NO_CACHE)
 mitkFunctionAddExternalProject(NAME Boost     ON           NO_CACHE)
 mitkFunctionAddExternalProject(NAME ZLIB      OFF          ADVANCED)
-mitkFunctionAddExternalProject(NAME cpprestsdk OFF         ADVANCED)
+mitkFunctionAddExternalProject(NAME cpprestsdk OFF         DEPENDS Boost ZLIB ADVANCED)
 mitkFunctionAddExternalProject(NAME ACVD      OFF          DOC "Use Approximated Centroidal Voronoi Diagrams")
 mitkFunctionAddExternalProject(NAME CTK       ON           DEPENDS Qt5 DCMTK DOC "Use CTK in MITK")
 mitkFunctionAddExternalProject(NAME Rasqal    OFF          DEPENDS Raptor2 PCRE ADVANCED)
 mitkFunctionAddExternalProject(NAME Redland   OFF          DEPENDS Rasqal DOC "Use the Redland RDF library")
 mitkFunctionAddExternalProject(NAME DCMQI     ON           DEPENDS DCMTK ITK DOC "Use dcmqi in MITK")
 mitkFunctionAddExternalProject(NAME MatchPoint  OFF ADVANCED  DEPENDS ITK DOC "Use the MatchPoint translation image registration library")
 
 if(MITK_USE_Qt5)
   mitkFunctionAddExternalProject(NAME Qwt     ON  ADVANCED DEPENDS Qt5)
 endif()
diff --git a/CMakeExternals/ZLIB.cmake b/CMakeExternals/ZLIB.cmake
index 5fc2155ad7..507c64e7f3 100644
--- a/CMakeExternals/ZLIB.cmake
+++ b/CMakeExternals/ZLIB.cmake
@@ -1,24 +1,27 @@
 set(proj ZLIB)
 set(proj_DEPENDENCIES "")
 
 if(MITK_USE_${proj})
   set(${proj}_DEPENDS ${proj})
 
   if(DEFINED ${proj}_DIR AND NOT EXISTS ${${proj}_DIR})
     message(FATAL_ERROR "${proj}_DIR variable is defined but corresponds to non-existing directory!")
   endif()
 
-  if(NOT DEFINED ${proj}_DIR)
+  find_package(ZLIB QUIET)
+
+  if(NOT DEFINED ${proj}_DIR AND NOT ZLIB_FOUND)
     ExternalProject_Add(${proj}
       GIT_REPOSITORY https://github.com/madler/zlib.git
       GIT_TAG v1.2.11
       CMAKE_ARGS ${ep_common_args}
       CMAKE_CACHE_ARGS ${ep_common_cache_args}
       CMAKE_CACHE_DEFAULT_ARGS ${ep_common_cache_default_args}
+      DEPENDS ${proj_DEPENDENCIES}
     )
 
     set(${proj}_DIR ${ep_prefix})
   else()
     mitkMacroEmptyExternalProject(${proj} "${proj_DEPENDENCIES}")
   endif()
 endif()
diff --git a/CMakeExternals/cpprestsdk.cmake b/CMakeExternals/cpprestsdk.cmake
index bb09838c5a..3e11bc1802 100644
--- a/CMakeExternals/cpprestsdk.cmake
+++ b/CMakeExternals/cpprestsdk.cmake
@@ -1,51 +1,46 @@
 set(proj cpprestsdk)
-set(proj_DEPENDENCIES Boost)
-
-find_package(ZLIB QUIET)
-
-if(NOT ZLIB_FOUND)
-  list(APPEND proj_DEPENDENCIES ZLIB)
-endif()
+set(proj_DEPENDENCIES Boost ZLIB)
 
 if(MITK_USE_${proj})
   set(${proj}_DEPENDS ${proj})
 
   if(DEFINED ${proj}_DIR AND NOT EXISTS ${${proj}_DIR})
     message(FATAL_ERROR "${proj}_DIR variable is defined but corresponds to non-existing directory!")
   endif()
 
   if(NOT DEFINED ${proj}_DIR)
     set(cmake_cache_args
       ${ep_common_cache_args}
       -DBUILD_SAMPLES:BOOL=OFF
       -DBUILD_TESTS:BOOL=OFF
       -DWERROR:BOOL=OFF
     )
 
     if(OPENSSL_ROOT_DIR)
       list(APPEND cmake_cache_args
         -DOPENSSL_ROOT_DIR:PATH=${OPENSSL_ROOT_DIR}
       )
     endif()
 
     ExternalProject_Add(${proj}
       GIT_REPOSITORY https://github.com/Microsoft/cpprestsdk.git
       GIT_TAG v2.10.10
       SOURCE_SUBDIR Release
       CMAKE_ARGS ${ep_common_args}
       CMAKE_CACHE_ARGS ${cmake_cache_args}
       CMAKE_CACHE_DEFAULT_ARGS ${ep_common_cache_default_args}
+      DEPENDS ${proj_DEPENDENCIES}
     )
 
     ExternalProject_Add_Step(${proj} git-submodule
       COMMAND ${GIT_EXECUTABLE} submodule update --init -- Release/libs/websocketpp
       WORKING_DIRECTORY <SOURCE_DIR>
       DEPENDEES patch
       DEPENDERS configure
     )
 
     set(${proj}_DIR ${ep_prefix})
   else()
     mitkMacroEmptyExternalProject(${proj} "${proj_DEPENDENCIES}")
   endif()
 endif()