sage build error

[Bruce]

Trying build sage I get the following error:

[reference] updating environment: 2 added, 0 changed, 0 removed
[reference] reading sources... [ 50%] index
[reference] reading sources... [100%] todolist
[reference] Merging environment/index files...
[reference] algebras: 2 todos, 16 index, 5 citations, 416 modules
[reference] arithgroup: 0 todos, 12 index, 9 citations, 295 modules
[reference] calculus: 2 todos, 23 index, 2 citations, 438 modules
[reference] categories: 13 todos, 130 index, 6 citations, 567 modules
[reference] cmd: 0 todos, 6 index, 0 citations, 277 modules
[reference] coding: 0 todos, 10 index, 6 citations, 576 modules
[reference] coercion: 0 todos, 4 index, 0 citations, 579 modules
./sage: line 134: 75966 Killed: 9 "$SAGE_ROOT/src/bin/sage" "$@"
gmake: *** [doc-html] Error 137
*** [do-build] Error code 1

Stop in /usr/ports/math/sage.
*** [install] Error code 1

Stop in /usr/ports/math/sage.