diff --git a/doc/errors/gluing.md b/doc/errors/gluing.md
new file mode 100644
index 000000000..111f8406c
--- /dev/null
+++ b/doc/errors/gluing.md
@@ -0,0 +1,27 @@
+## unsupported token gluing `foo + bar`
+
+There was a problem in an expression using +, e.g. `foo + bar`.
+This can be due to two causes, check which one applies in your case.
+
+1. You are trying to use + on runtime arguments. Even if you are using
+`foo + bar` in an oper, make sure that the oper isn't called in a
+linearization that takes arguments. Both of the following are illegal:
+
+    lin Test foo bar = foo.s + bar.s          -- explicit + in a lin
+    lin Test foo bar = opWithPlus foo bar     -- the oper uses +
+
+2. One of the arguments in `foo + bar` is a bound variable
+from pattern matching a string, but the cases are non-exhaustive.
+Example:
+    case "test" of {
+      x + "a" => x + "b"   -- no applicable case for "test", so x = ???
+    } ;
+
+You can fix this by adding a catch-all case in the end:
+    { x + "a" => x + "b" ;
+      _       => "default case" } ;
+
+3. If neither applies to your problem, submit a bug report and we
+will update the error message and this documentation.
+
+    https://github.com/GrammaticalFramework/gf-core/issues
diff --git a/src/compiler/GF/Compile/Compute/ConcreteNew.hs b/src/compiler/GF/Compile/Compute/ConcreteNew.hs
index 9a8024697..ea55e77cb 100644
--- a/src/compiler/GF/Compile/Compute/ConcreteNew.hs
+++ b/src/compiler/GF/Compile/Compute/ConcreteNew.hs
@@ -297,29 +297,10 @@ glue env (v1,v2) = glu v1 v2
                             in error $ unlines
                                 [originalMsg
                                 ,""
-                                ,"There was a problem in the expression `" ++ term ++ "`"
-                                ,"This can be due to two causes, check which one applies in your case."
-                                ,""
-                                ,"1) You are trying to use + on runtime arguments. Even if you are using"
-                                ,"   `"++term++"` in an oper, make sure that the oper isn't called in a"
-                                ,"   linearization that takes arguments. Both of the following are illegal:"
-                                ,""
-                                ,"      lin Test foo bar = foo.s + bar.s          <- explicit + in a lin"
-                                ,"      lin Test foo bar = opWithPlus foo bar     <- the oper uses +"
-                                ,""
-                                ,"2) One of the arguments in `"++term++"` is a bound variable"
-                                ,"   from pattern matching a string, but the cases are non-exhaustive."
-                                ,"   Example:"
-                                ,"      case \"test\" of {"
-                                ,"        x + \"a\" => x + \"b\"   <- no applicable case for \"test\", so x = ???"
-                                ,"      } ;"
-                                ,""
-                                ,"   You can fix this by adding a catch-all case in the end:"
-                                ,"      { x + \"a\" => x + \"b\" ;"
-                                ,"        _       => \"default case\" } ;"
-                                ,""
-                                ,"3) If neither applies, submit a bug report and we update the error message."
-                                ,"      https://github.com/GrammaticalFramework/gf-core/issues"
+                                ,"There was a problem in the expression `"++term++"`, either:"
+                                ,"1) You are trying to use + on runtime arguments, possibly via an oper."
+                                ,"2) One of the arguments in `"++term++"` is a bound variable from pattern matching a string, but the cases are non-exhaustive."
+                                ,"For more help see https://github.com/GrammaticalFramework/gf-core/tree/master/doc/errors/gluing.md"
                                 ]