diff --git a/src/cell.cpp b/src/cell.cpp
index 6a962ecede..c1585862bc 100644
--- a/src/cell.cpp
+++ b/src/cell.cpp
@@ -424,7 +424,7 @@ CSGCell::distance(Position r, Direction u, int32_t on_surface) const
 
     // Calculate the distance to this surface.
     // Note the off-by-one indexing
-    bool coincident {token == on_surface};
+    bool coincident {std::abs(token) == std::abs(on_surface)};
     double d {model::surfaces[abs(token)-1]->distance(r, u, coincident)};
 
     // Check if this distance is the new minimum.
diff --git a/tools/ci/travis-install.sh b/tools/ci/travis-install.sh
index 10c168d129..2bca50e4b4 100755
--- a/tools/ci/travis-install.sh
+++ b/tools/ci/travis-install.sh
@@ -22,13 +22,8 @@ fi
 # Build and install OpenMC executable
 python tools/ci/travis-install.py
 
-if [[ $TRAVIS_PYTHON_VERSION == "3.7" ]]; then
-    # Install Python API in editable mode
-    pip install -e .[test]
-else
-    # Conditionally install vtk
-    pip install -e .[test,vtk]
-fi
+# Install Python API in editable mode
+pip install -e .[test,vtk]
 
 # For uploading to coveralls
 pip install coveralls