diff --git a/compiler/prog_io.m b/compiler/prog_io.m
index a54bd929f..5fdfdf4bd 100644
--- a/compiler/prog_io.m
+++ b/compiler/prog_io.m
@@ -1044,14 +1044,6 @@ parse_decl_attribute("all", [TVars, Decl],
 		quantifier(univ, TVarsList), Decl) :-
 	parse_list_of_vars(TVars, TVarsList).
 
-:- pred parse_list_of_vars(term, list(var)).
-:- mode parse_list_of_vars(in, out) is semidet.
-	
-parse_list_of_vars(term__functor(term__atom("[]"), [], _), []).
-parse_list_of_vars(term__functor(term__atom("."), [Head, Tail], _), [V|Vs]) :-
-	Head = term__variable(V),
-	parse_list_of_vars(Tail, Vs).
-
 :- pred check_no_attributes(maybe1(item), decl_attrs, maybe1(item)).
 :- mode check_no_attributes(in, in, out) is det.
 
diff --git a/compiler/prog_io_goal.m b/compiler/prog_io_goal.m
index a6cd8b3ac..3590fb34e 100644
--- a/compiler/prog_io_goal.m
+++ b/compiler/prog_io_goal.m
@@ -193,7 +193,7 @@ parse_goal_2("<=>", [A0, B0], V0, equivalent(A, B), V):-
 	parse_goal(B0, V1, B, V).
 
 parse_goal_2("some", [Vars0, A0], V0, some(Vars, A), V):-
-	term__vars(Vars0, Vars),
+	parse_list_of_vars(Vars0, Vars),
 	parse_goal(A0, V0, A, V).
 
 	% The following is a temporary hack to handle `is' in
@@ -227,9 +227,10 @@ parse_goal_with_purity(A0, V0, Purity, A, V) :-
 
 parse_some_vars_goal(A0, VarSet0, Vars, A, VarSet) :-
 	( 
-		A0 = term__functor(term__atom("some"), [Vars0, A1], _Context)
+		A0 = term__functor(term__atom("some"), [Vars0, A1], _Context),
+		parse_list_of_vars(Vars0, Vars1)
 	->
-		term__vars(Vars0, Vars),
+		Vars = Vars1,
 		parse_goal(A1, VarSet0, A, VarSet)
 	;
 		Vars = [],
diff --git a/compiler/prog_io_util.m b/compiler/prog_io_util.m
index d3b36d6a9..e63aec8ef 100644
--- a/compiler/prog_io_util.m
+++ b/compiler/prog_io_util.m
@@ -42,6 +42,14 @@
 :- pred add_context(maybe1(item), term__context, maybe_item_and_context).
 :- mode add_context(in, in, out) is det.
 
+%
+% Various predicates to parse small bits of syntax.
+% These predicates simply fail if they encounter a syntax error.
+%
+
+:- pred parse_list_of_vars(term, list(var)).
+:- mode parse_list_of_vars(in, out) is semidet.
+
 :- pred convert_mode_list(list(term), list(mode)).
 :- mode convert_mode_list(in, out) is semidet.
 
@@ -51,9 +59,6 @@
 :- pred convert_inst_list(list(term), list(inst)).
 :- mode convert_inst_list(in, out) is semidet.
 
-	% Parse an inst.
-	% Fails on syntax errors.
-	%
 :- pred convert_inst(term, inst).
 :- mode convert_inst(in, out) is semidet.
 
@@ -102,6 +107,11 @@
 add_context(error(M, T), _, error(M, T)).
 add_context(ok(Item), Context, ok(Item, Context)).
 
+parse_list_of_vars(term__functor(term__atom("[]"), [], _), []).
+parse_list_of_vars(term__functor(term__atom("."), [Head, Tail], _), [V|Vs]) :-
+	Head = term__variable(V),
+	parse_list_of_vars(Tail, Vs).
+
 convert_mode_list([], []).
 convert_mode_list([H0|T0], [H|T]) :-
 	convert_mode(H0, H),
diff --git a/compiler/typecheck.m b/compiler/typecheck.m
index 441f85d37..d5e0bc1f7 100644
--- a/compiler/typecheck.m
+++ b/compiler/typecheck.m
@@ -4705,6 +4705,14 @@ report_error_undef_pred(TypeCheckInfo, PredCallId) -->
 		;
 			[]
 		)
+	;
+		{ PredName = unqualified("some"), Arity = 2 }
+	->
+		io__write_string(
+		    "  syntax error in existential quantification: first\n"),
+		prog_out__write_context(Context),
+		io__write_string(
+		    "  argument of `some' should be a list of variables.\n")
 	;
 		io__write_string("  error: undefined predicate `"),
 		hlds_out__write_pred_call_id(PredCallId),
@@ -4977,6 +4985,8 @@ language_builtin("<=", 2).
 language_builtin("call", _).
 language_builtin("impure", 1).
 language_builtin("semipure", 1).
+language_builtin("all", 2).
+language_builtin("some", 2).
 
 :- pred write_call_context(term__context, pred_call_id, int, unify_context,
 				io__state, io__state).
diff --git a/tests/invalid/Mmakefile b/tests/invalid/Mmakefile
index cb270bdc6..34a0ab6ad 100644
--- a/tests/invalid/Mmakefile
+++ b/tests/invalid/Mmakefile
@@ -41,6 +41,7 @@ SOURCES= \
 	prog_io_erroneous.m \
 	qual_basic_test2.m \
 	qualified_cons_id2.m \
+	some.m \
 	spurious_mode_error.m \
 	test_nested.m \
 	type_inf_loop.m \
diff --git a/tests/invalid/some.err_exp b/tests/invalid/some.err_exp
new file mode 100644
index 000000000..9a8103bbe
--- /dev/null
+++ b/tests/invalid/some.err_exp
@@ -0,0 +1,14 @@
+some.m:006: Error: unrecognized declaration: some junk pred p2(int :: in) is semidet.
+some.m:012: In clause for predicate `some:p1/1':
+some.m:012:   in argument 1 of call to predicate `some/2':
+some.m:012:   error: undefined symbol `junk/0'.
+some.m:012: In clause for predicate `some:p1/1':
+some.m:012:   syntax error in existential quantification: first
+some.m:012:   argument of `some' should be a list of variables.
+some.m:013: In clause for predicate `some:p3/1':
+some.m:013:   in argument 1 of call to predicate `some/2':
+some.m:013:   error: undefined symbol `junk/0'.
+some.m:013: In clause for predicate `some:p3/1':
+some.m:013:   syntax error in existential quantification: first
+some.m:013:   argument of `some' should be a list of variables.
+For more information, try recompiling with `-E'.
diff --git a/tests/invalid/some.m b/tests/invalid/some.m
new file mode 100644
index 000000000..c64f7e0aa
--- /dev/null
+++ b/tests/invalid/some.m
@@ -0,0 +1,14 @@
+:- module (some).
+
+:- interface.
+
+:- pred p1(int::in) is semidet.
+:- some junk pred p2(int::in) is semidet.
+:- pred p3(int::in) is semidet.
+
+:- implementation.
+:- import_module int.
+
+p1(X) :- some junk p3(X).
+p3(X) :- ( some junk X > 0 -> X = 42 ; X = -42 ).
+