diff --git a/src/IO/CMakeLists.txt b/src/IO/CMakeLists.txt
index ef8e53e6da..90f4115f40 100644
--- a/src/IO/CMakeLists.txt
+++ b/src/IO/CMakeLists.txt
@@ -83,9 +83,9 @@ endif()
 if (CERN_ROOT_FOUND)
   target_include_directories(IO PRIVATE ${CERN_ROOT_INCLUDE_DIRS})
   if (TARGET ROOT::Tree)
-   target_link_libraries(IO PUBLIC ROOT::Tree)
+   target_link_libraries(IO PRIVATE ROOT::Tree)
   else()
-   target_link_libraries(IO PUBLIC ${CERN_ROOT_LIBRARIES})
+   target_link_libraries(IO PRIVATE ${CERN_ROOT_LIBRARIES})
   endif()
 endif()
 
@@ -94,12 +94,12 @@ if (HAVE_HDF5)
 endif()
 
 if (HAVE_ITK)
-  target_link_libraries(IO PUBLIC ITKCommon ${ITK_LIBRARIES})
+  target_link_libraries(IO PRIVATE ITKCommon ${ITK_LIBRARIES})
 endif()
 
 if (UPENN_FOUND)
   target_include_directories(IO PUBLIC ${UPENN_INCLUDE_DIR})
-  target_link_libraries(IO PUBLIC ${UPENN_libsss_tof} ${UPENN_libfit} ${UPENN_libdist} ${UPENN_libgeom}
+  target_link_libraries(IO PRIVATE ${UPENN_libsss_tof} ${UPENN_libfit} ${UPENN_libdist} ${UPENN_libgeom}
         ${UPENN_liblor} ${UPENN_liblist} ${UPENN_libmhdr} ${JANSSON_LIBRARY} ${ZLIB_LIBRARY_RELEASE}
 ${UPENN_libimagio} ${UPENN_libimagio++})
 endif()
diff --git a/src/cmake/STIRConfig.cmake.in b/src/cmake/STIRConfig.cmake.in
index 52fd60b592..89594b9cbd 100644
--- a/src/cmake/STIRConfig.cmake.in
+++ b/src/cmake/STIRConfig.cmake.in
@@ -63,15 +63,24 @@ else()
 endif()
 
 ## find external packages
+# Note that we generally need find_package even for those that are only
+# PRIVATE dependencies (such as ITK, parallelproj etc). This is because
+# otherwise their targets (such as parallelproj::parallelproj_c) don't exist,
+# and the user will get CMake errors.
+# See https://github.com/UCL/STIR/issues/1535
+
 # we use a trick by Matt McCormick (kitware)
 # to set ITK_DIR etc first before calling find_package
 # to make sure we pick the same version of the external library
+
 if (STIR_FIND_QUIETLY)
   SET(STIR_FIND_TYPE "QUIET")
 else()
   SET(STIR_FIND_TYPE "REQUIRED")
 endif()
 
+find_package(Boost @Boost_VERSION@ REQUIRED)
+
 if (@ITK_FOUND@)
   message(STATUS "ITK support in STIR enabled.")
   set(ITK_DIR "@ITK_DIR@")
@@ -79,7 +88,6 @@ if (@ITK_FOUND@)
   if(NOT ITK_FOUND)
     SET(STIR_FOUND OFF)
   endif()
-  include(${ITK_USE_FILE})
   set(STIR_BUILT_WITH_ITK TRUE)
 endif()
 
diff --git a/src/recon_buildblock/CMakeLists.txt b/src/recon_buildblock/CMakeLists.txt
index 61286275f7..ae64f14fce 100644
--- a/src/recon_buildblock/CMakeLists.txt
+++ b/src/recon_buildblock/CMakeLists.txt
@@ -147,19 +147,19 @@ endif()
 target_link_libraries(recon_buildblock PUBLIC modelling_buildblock display numerics_buildblock listmode_buildblock data_buildblock buildblock spatial_transformation_buildblock )
 
 if (STIR_WITH_NiftyPET_PROJECTOR)
-	target_link_libraries(recon_buildblock PUBLIC NiftyPET::petprj)
-	target_link_libraries(recon_buildblock PUBLIC NiftyPET::mmr_auxe)
-	target_link_libraries(recon_buildblock PUBLIC NiftyPET::mmr_lmproc)
-	target_link_libraries(recon_buildblock PUBLIC CUDA::cudart)
+	target_link_libraries(recon_buildblock PRIVATE NiftyPET::petprj)
+	target_link_libraries(recon_buildblock PRIVATE NiftyPET::mmr_auxe)
+	target_link_libraries(recon_buildblock PRIVATE NiftyPET::mmr_lmproc)
+	target_link_libraries(recon_buildblock PRIVATE CUDA::cudart)
 endif()
 
 if (STIR_WITH_Parallelproj_PROJECTOR)
-  target_link_libraries(recon_buildblock PUBLIC parallelproj::parallelproj_c)
+  target_link_libraries(recon_buildblock PRIVATE parallelproj::parallelproj_c)
   if (parallelproj_built_with_CUDA)
-    target_link_libraries(recon_buildblock PUBLIC parallelproj::parallelproj_cuda)
+    target_link_libraries(recon_buildblock PRIVATE parallelproj::parallelproj_cuda)
   endif()
 endif()
 
 if (STIR_WITH_CUDA)
-  target_link_libraries(recon_buildblock PUBLIC CUDA::cudart)
-endif()
\ No newline at end of file
+  target_link_libraries(recon_buildblock PRIVATE CUDA::cudart)
+endif()