diff --git a/Modules/ThirdParty/Eigen3/CMakeLists.txt b/Modules/ThirdParty/Eigen3/CMakeLists.txt
index 794c615be55..acd29f41a42 100644
--- a/Modules/ThirdParty/Eigen3/CMakeLists.txt
+++ b/Modules/ThirdParty/Eigen3/CMakeLists.txt
@@ -55,7 +55,18 @@ if(ITK_USE_SYSTEM_EIGEN)
   )
 else()
   set(ITKEigen3_LIBRARIES eigen_internal)
-  set(ITKEigen3_INCLUDE_DIRS ${ITKEigen3_SOURCE_DIR}/src)
+  # Two include directories are required so both ITK's own
+  # ITK_EIGEN(X) macro convention <itkeigen/Eigen/X> and the upstream
+  # Eigen convention <Eigen/X> resolve.  ITK code rooted at
+  # ${ITKEigen3_SOURCE_DIR}/src uses the macro form; external
+  # consumers (proxTV, anything else that includes Eigen the
+  # standard way) need the parent of <Eigen/X>, which is
+  # ${ITKEigen3_SOURCE_DIR}/src/itkeigen.
+  set(
+    ITKEigen3_INCLUDE_DIRS
+    ${ITKEigen3_SOURCE_DIR}/src
+    ${ITKEigen3_SOURCE_DIR}/src/itkeigen
+  )
 endif()
 
 # For the generated itk_eigen.h