diff --git a/catkin_virtualenv/cmake/catkin_generate_virtualenv.cmake b/catkin_virtualenv/cmake/catkin_generate_virtualenv.cmake
index 39d847e..22a283b 100644
--- a/catkin_virtualenv/cmake/catkin_generate_virtualenv.cmake
+++ b/catkin_virtualenv/cmake/catkin_generate_virtualenv.cmake
@@ -33,29 +33,6 @@ function(catkin_generate_virtualenv)
   set(${PROJECT_NAME}_VENV_DEVEL_DIR ${venv_devel_dir} PARENT_SCOPE)
   set(${PROJECT_NAME}_VENV_INSTALL_DIR ${venv_install_dir} PARENT_SCOPE)
 
-  if(${ARG_PYTHON3})
-    set(build_venv_extra "--python3")
-    set(PYTHON_VERSION_MAJOR 3)
-  endif()
-
-  if(NOSETESTS)
-    if(${ARG_PYTHON3})
-      find_program(nosetests NAMES
-        "nosetests${PYTHON_VERSION_MAJOR}"
-        "nosetests-${PYTHON_VERSION_MAJOR}"
-        "nosetests")
-    else()
-      set(nosetests ${NOSETESTS})
-    endif()
-
-    set(nosetests "${venv_devel_dir}/bin/python${PYTHON_VERSION_MAJOR} ${nosetests}")
-
-    # (pbovbel): NOSETESTS originally set by catkin here:
-    # <https://github.com/ros/catkin/blob/kinetic-devel/cmake/test/nosetests.cmake#L86>
-    message(STATUS "Using virtualenv to run Python nosetests: ${nosetests}")
-    set(NOSETESTS ${nosetests} PARENT_SCOPE)
-  endif()
-
   # Collect all exported pip requirements files, from this package and all dependencies
   execute_process(
     COMMAND ${CATKIN_ENV} ${PYTHON_EXECUTABLE} ${catkin_virtualenv_CMAKE_DIR}/glob_requirements.py --package-name ${PROJECT_NAME}
@@ -63,6 +40,13 @@ function(catkin_generate_virtualenv)
     OUTPUT_STRIP_TRAILING_WHITESPACE
   )
 
+  # Extra python 3 compatibility flags
+  if(${ARG_PYTHON3})
+    set(build_venv_extra "--python3")
+    set(PYTHON_VERSION_MAJOR 3)
+    list(APPEND requirements_list ${catkin_virtualenv_CMAKE_DIR}/python3_requirements.txt)
+  endif()
+
   set(generated_requirements ${CMAKE_BINARY_DIR}/generated_requirements.txt)
 
   foreach(requirements_txt ${requirements_list})
@@ -90,6 +74,7 @@ function(catkin_generate_virtualenv)
     DEPENDS ${generated_requirements}
   )
 
+  # Per-package virtualenv target
   add_custom_target(${PROJECT_NAME}_generate_virtualenv ALL
     DEPENDS ${CMAKE_BINARY_DIR}/${venv_dir}
     DEPENDS ${venv_devel_dir}
@@ -103,4 +88,22 @@ function(catkin_generate_virtualenv)
   install(FILES ${generated_requirements}
     DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION})
 
+  if(NOSETESTS)
+    if(${ARG_PYTHON3})
+      find_program(nosetests NAMES
+        "nosetests${PYTHON_VERSION_MAJOR}"
+        "nosetests-${PYTHON_VERSION_MAJOR}"
+        "nosetests")
+    else()
+      set(nosetests ${NOSETESTS})
+    endif()
+
+    set(nosetests "${venv_devel_dir}/bin/python${PYTHON_VERSION_MAJOR} ${nosetests}")
+
+    # (pbovbel): NOSETESTS originally set by catkin here:
+    # <https://github.com/ros/catkin/blob/kinetic-devel/cmake/test/nosetests.cmake#L86>
+    message(STATUS "Using virtualenv to run Python nosetests: ${nosetests}")
+    set(NOSETESTS ${nosetests} PARENT_SCOPE)
+    endif()
+
 endfunction()
diff --git a/catkin_virtualenv/cmake/combine_requirements.py b/catkin_virtualenv/cmake/combine_requirements.py
index 6fb87ed..4279348 100644
--- a/catkin_virtualenv/cmake/combine_requirements.py
+++ b/catkin_virtualenv/cmake/combine_requirements.py
@@ -41,6 +41,9 @@ def combine_requirements(requirements_list, output_file):
                     combined_requirements[requirement.name] = combined_requirements[requirement.name] + requirement
                 except KeyError:
                     combined_requirements[requirement.name] = requirement
+                except requirements.ReqMergeException as e:
+                    print("In files {}: {}".format(requirements_list, e), file=sys.stderr)
+                    raise
 
     for requirement in combined_requirements.values():
         output_file.write("{}\n".format(requirement))
diff --git a/catkin_virtualenv/cmake/python3_requirements.txt b/catkin_virtualenv/cmake/python3_requirements.txt
new file mode 100644
index 0000000..991d95a
--- /dev/null
+++ b/catkin_virtualenv/cmake/python3_requirements.txt
@@ -0,0 +1,2 @@
+rospkg==1.1.4
+catkin-pkg==0.3.9
diff --git a/test_catkin_virtualenv_py3/requirements.txt b/test_catkin_virtualenv_py3/requirements.txt
index 0b096b7..55df76d 100644
--- a/test_catkin_virtualenv_py3/requirements.txt
+++ b/test_catkin_virtualenv_py3/requirements.txt
@@ -1,3 +1 @@
 wrapt==1.10.10
-rospkg==1.1.4
-catkin-pkg==0.3.9