diff --git a/userspace/digwatch/lua/compiler.lua b/userspace/digwatch/lua/compiler.lua
index e9a0215f..a976fbe7 100644
--- a/userspace/digwatch/lua/compiler.lua
+++ b/userspace/digwatch/lua/compiler.lua
@@ -225,7 +225,7 @@ local G = {
   idRest = alnum + P("_");
   Identifier = V"idStart" * V"idRest"^0;
   Macro = V"idStart" * V"idRest"^0 * -P".";
-  FieldName = V"Identifier" * (P"." + V"Identifier")^1;
+  FieldName = V"Identifier" * (P"." + V"Identifier")^1 * (P"[" * V"Int" * P"]")^-1;
   Name = C(V"Identifier") * -V"idRest";
   Hex = (P("0x") + P("0X")) * xdigit^1;
   Expo = S("eE") * S("+-")^-1 * digit^1;
@@ -374,7 +374,7 @@ function expand_macros(ast, defs, changed)
 
       if (ast.right.type == "Macro") then
          if (defs[ast.right.value] == nil) then
-            error("Undefined macro ".. ast.right.value .. "used in filter.")
+            error("Undefined macro ".. ast.right.value .. " used in filter.")
          end
          ast.right = copy(defs[ast.right.value])
          changed = true
@@ -387,7 +387,7 @@ function expand_macros(ast, defs, changed)
    elseif ast.type == "UnaryBoolOp" then
       if (ast.argument.type == "Macro") then
          if (defs[ast.argument.value] == nil) then
-            error("Undefined macro ".. ast.argument.value .. "used in filter.")
+            error("Undefined macro ".. ast.argument.value .. " used in filter.")
          end
          ast.argument = copy(defs[ast.argument.value])
          changed = true
diff --git a/userspace/digwatch/lua/smoke.sh b/userspace/digwatch/lua/smoke.sh
index d4db4885..8ba7b357 100755
--- a/userspace/digwatch/lua/smoke.sh
+++ b/userspace/digwatch/lua/smoke.sh
@@ -60,6 +60,10 @@ good "a.b = a.a"
 good "a.b = a.a |"
 good "a.b = a.a | %evt.type %fd.num blabla"
 
+good "evt.arg[0] contains /bin"
+bad "evt.arg[a] contains /bin"
+bad "evt.arg[] contains /bin"
+
 bad "a.g in ()"
 bad "a.b = b = 1"
 bad "(a.b = 1"