diff --git a/loopy/transform/instruction.py b/loopy/transform/instruction.py
index 92bcb0bf4b230a435ba0729fb48aec52063eae19..7c9c9688604179dce2aa7dcd6954d76a0df32cc7 100644
--- a/loopy/transform/instruction.py
+++ b/loopy/transform/instruction.py
@@ -92,13 +92,18 @@ def add_dependency(kernel, insn_match, depends_on):
     if isinstance(depends_on, str) and depends_on in kernel.id_to_insn:
         added_deps = frozenset([depends_on])
     else:
-        added_deps = find_instructions(depends_on)
+        added_deps = frozenset(
+                dep.id for dep in find_instructions(kernel, depends_on))
 
     if not added_deps:
-        raise LoopyError("no instructions found matching '%s'" % depends_on)
+        raise LoopyError("no instructions found matching '%s' "
+                "(to add as dependencies)" % depends_on)
+
+    matched = [False]
 
     def add_dep(insn):
         new_deps = insn.depends_on
+        matched[0] = True
         if new_deps is None:
             new_deps = added_deps
         else:
@@ -106,7 +111,13 @@ def add_dependency(kernel, insn_match, depends_on):
 
         return insn.copy(depends_on=new_deps)
 
-    return map_instructions(kernel, insn_match, add_dep)
+    result = map_instructions(kernel, insn_match, add_dep)
+
+    if not matched[0]:
+        raise LoopyError("no instructions found matching '%s' "
+                "(to which dependencies would be added)" % insn_match)
+
+    return result
 
 # }}}
 
diff --git a/loopy/transform/precompute.py b/loopy/transform/precompute.py
index 5ab9dfab3c8ac0669c3e7eaf4091bb3ab4b0e2a2..a19e06ecdf7c9966501ebb9600ea4e01614363f4 100644
--- a/loopy/transform/precompute.py
+++ b/loopy/transform/precompute.py
@@ -799,7 +799,7 @@ def precompute(kernel, subst_use, sweep_inames=[], within=None,
 
     if temporary_scope == temp_var_scope.GLOBAL:
         barrier_insn_id = kernel.make_unique_instruction_id(
-                based_on=c_subst_name+"_b")
+                based_on=c_subst_name+"_barrier")
         from loopy.kernel.instruction import BarrierInstruction
         barrier_insn = BarrierInstruction(
                 id=barrier_insn_id,
diff --git a/test/test_reduction.py b/test/test_reduction.py
index fec72138da24d41cc14da357ebe596b189b5d2f4..820c669da494f4d8863d274120cd5c0c7eb4420f 100644
--- a/test/test_reduction.py
+++ b/test/test_reduction.py
@@ -239,7 +239,7 @@ def test_global_parallel_reduction(ctx_factory, size):
     knl = lp.realize_reduction(knl)
     knl = lp.add_dependency(
             knl, "writes:acc_i_outer",
-            "red_i_outer_arg_b")
+            "id:red_i_outer_arg_barrier")
 
     lp.auto_test_vs_ref(
             ref_knl, ctx, knl, parameters={"n": size},
@@ -279,7 +279,7 @@ def test_global_mc_parallel_reduction(ctx_factory, size):
     knl = lp.realize_reduction(knl)
     knl = lp.add_dependency(
             knl, "writes:acc_i_outer",
-            "red_i_outer_arg_b")
+            "id:red_i_outer_arg_barrier")
 
     lp.auto_test_vs_ref(
             ref_knl, ctx, knl, parameters={"n": size})