diff --git a/lib/hex_solver/assignment.ex b/lib/hex_solver/assignment.ex
index 58271b5..74ba494 100644
--- a/lib/hex_solver/assignment.ex
+++ b/lib/hex_solver/assignment.ex
@@ -1,7 +1,7 @@
 defmodule HexSolver.Assignment do
   @moduledoc false
 
-  alias HexSolver.{Assignment, Term}
+  alias HexSolver.{Assignment, Incompatibility, Term}
 
   defstruct term: nil,
             decision_level: nil,
@@ -17,7 +17,7 @@ defmodule HexSolver.Assignment do
   end
 
   def to_string(%Assignment{term: term}) do
-    Kernel.to_string(term)
+    Term.to_string(term)
   end
 
   defimpl String.Chars do
@@ -34,10 +34,10 @@ defmodule HexSolver.Assignment do
           },
           _opts
         ) do
-      "#Assignment<term: #{term}#{maybe(", cause: ", cause)}, level: #{decision_level}, index: #{index}>"
+      "#Assignment<term: #{Term.to_string(term)}#{maybe(", cause: ", cause)}, level: #{decision_level}, index: #{index}>"
     end
 
     defp maybe(_prefix, nil), do: ""
-    defp maybe(prefix, value), do: "#{prefix}#{value}"
+    defp maybe(prefix, value), do: "#{prefix}#{Incompatibility.to_string(value)}"
   end
 end
diff --git a/lib/hex_solver/constraint.ex b/lib/hex_solver/constraint.ex
index a81714d..0071329 100644
--- a/lib/hex_solver/constraint.ex
+++ b/lib/hex_solver/constraint.ex
@@ -11,4 +11,5 @@ defprotocol HexSolver.Constraint do
   def union(left, right)
   def compare(left, right)
   def to_requirement(constraint)
+  def to_string(constraint)
 end
diff --git a/lib/hex_solver/constraints/impl.ex b/lib/hex_solver/constraints/impl.ex
index 8e4f092..6597b2e 100644
--- a/lib/hex_solver/constraints/impl.ex
+++ b/lib/hex_solver/constraints/impl.ex
@@ -35,6 +35,9 @@ defmodule HexSolver.Constraints.Impl do
 
         def to_requirement(constraint),
           do: unquote(__CALLER__.module).to_requirement(constraint)
+
+        def to_string(constraint),
+          do: unquote(__CALLER__.module).to_string(constraint)
       end
     end
   end
diff --git a/lib/hex_solver/constraints/range.ex b/lib/hex_solver/constraints/range.ex
index 76e77d1..86f72d2 100644
--- a/lib/hex_solver/constraints/range.ex
+++ b/lib/hex_solver/constraints/range.ex
@@ -440,7 +440,7 @@ defmodule HexSolver.Constraints.Range do
 
   defimpl Inspect do
     def inspect(range, _opts) do
-      "#Range<#{range}>"
+      "#Range<#{HexSolver.Constraints.Range.to_string(range)}>"
     end
   end
 end
diff --git a/lib/hex_solver/constraints/union.ex b/lib/hex_solver/constraints/union.ex
index c678da9..0db6356 100644
--- a/lib/hex_solver/constraints/union.ex
+++ b/lib/hex_solver/constraints/union.ex
@@ -157,7 +157,7 @@ defmodule HexSolver.Constraints.Union do
   end
 
   def to_string(%Union{ranges: ranges}) do
-    Enum.map_join(ranges, " or ", &Kernel.to_string/1)
+    Enum.map_join(ranges, " or ", &Constraint.to_string/1)
   end
 
   defimpl String.Chars do
@@ -166,7 +166,7 @@ defmodule HexSolver.Constraints.Union do
 
   defimpl Inspect do
     def inspect(union, _opts) do
-      "#Union<#{union}>"
+      "#Union<#{HexSolver.Constraints.Union.to_string(union)}>"
     end
   end
 end
diff --git a/lib/hex_solver/constraints/version.ex b/lib/hex_solver/constraints/version.ex
index e42f499..b8db504 100644
--- a/lib/hex_solver/constraints/version.ex
+++ b/lib/hex_solver/constraints/version.ex
@@ -103,6 +103,10 @@ defmodule HexSolver.Constraints.Version do
     Kernel.to_string(version)
   end
 
+  def to_string(%Version{} = version) do
+    Kernel.to_string(version)
+  end
+
   def max(left, right) do
     case compare(left, right) do
       :lt -> right
diff --git a/lib/hex_solver/incompatibility.ex b/lib/hex_solver/incompatibility.ex
index 8783d15..39b22c5 100644
--- a/lib/hex_solver/incompatibility.ex
+++ b/lib/hex_solver/incompatibility.ex
@@ -73,7 +73,7 @@ defmodule HexSolver.Incompatibility do
   def to_string(%Incompatibility{cause: :no_versions, terms: terms}, opts) do
     [%Term{positive: true} = term] = terms
 
-    "no versions of #{package_name(term, opts)} match #{bright(term.package_range.constraint, opts)}"
+    "no versions of #{package_name(term, opts)} match #{bright(Constraint.to_string(term.package_range.constraint), opts)}"
   end
 
   def to_string(%Incompatibility{cause: :package_not_found, terms: terms}, opts) do
@@ -83,7 +83,8 @@ defmodule HexSolver.Incompatibility do
 
   def to_string(%Incompatibility{cause: :root, terms: terms}, opts) do
     [%Term{positive: false} = term] = terms
-    "#{package_name(term, opts)} is #{bright(term.package_range.constraint, opts)}"
+
+    "#{package_name(term, opts)} is #{bright(Constraint.to_string(term.package_range.constraint), opts)}"
   end
 
   def to_string(%Incompatibility{terms: []}, _opts) do
@@ -409,7 +410,7 @@ defmodule HexSolver.Incompatibility do
 
   defp term_abs(%Term{} = term), do: %Term{term | positive: true}
 
-  defp bright_term_abs(term, opts), do: bright(term_abs(term), opts)
+  defp bright_term_abs(term, opts), do: bright(Term.to_string(term_abs(term)), opts)
 
   defimpl String.Chars do
     defdelegate to_string(incompatibility), to: HexSolver.Incompatibility
diff --git a/lib/hex_solver/package_range.ex b/lib/hex_solver/package_range.ex
index 0697d84..8e0a867 100644
--- a/lib/hex_solver/package_range.ex
+++ b/lib/hex_solver/package_range.ex
@@ -1,7 +1,7 @@
 defmodule HexSolver.PackageRange do
   @moduledoc false
 
-  alias HexSolver.PackageRange
+  alias HexSolver.{Constraint, PackageRange}
   alias HexSolver.Constraints.Range
 
   defstruct repo: nil,
@@ -18,7 +18,7 @@ defmodule HexSolver.PackageRange do
     do: "#{repo}/#{name}#{constraint(constraint)}"
 
   defp constraint(%Range{min: nil, max: nil}), do: ""
-  defp constraint(constraint), do: " #{constraint}"
+  defp constraint(constraint), do: " " <> Constraint.to_string(constraint)
 
   defimpl String.Chars do
     defdelegate to_string(package_range), to: HexSolver.PackageRange
@@ -26,9 +26,9 @@ defmodule HexSolver.PackageRange do
 
   defimpl Inspect do
     def inspect(%{repo: nil, name: name, constraint: constraint}, _opts),
-      do: "#PackageRange<#{name} #{constraint}>"
+      do: "#PackageRange<#{name} #{Constraint.to_string(constraint)}>"
 
     def inspect(%{repo: repo, name: name, constraint: constraint}, _opts),
-      do: "#PackageRange<#{repo}/#{name} #{constraint}>"
+      do: "#PackageRange<#{repo}/#{name} #{Constraint.to_string(constraint)}>"
   end
 end
diff --git a/lib/hex_solver/solver.ex b/lib/hex_solver/solver.ex
index 43bc97f..0845cce 100644
--- a/lib/hex_solver/solver.ex
+++ b/lib/hex_solver/solver.ex
@@ -2,6 +2,7 @@ defmodule HexSolver.Solver do
   @moduledoc false
 
   alias HexSolver.{
+    Assignment,
     Incompatibility,
     PackageLister,
     PackageRange,
@@ -96,7 +97,7 @@ defmodule HexSolver.Solver do
   defp propagate_incompatibility([], unsatisfied, incompatibility, state, _opts) do
     # Only one term in the incompatibility was unsatisfied
     unsatisfied = %{unsatisfied | positive: not unsatisfied.positive}
-    Logger.debug("RESOLVER: derived #{unsatisfied}")
+    Logger.debug("RESOLVER: derived #{Term.to_string(unsatisfied)}")
 
     solution = PartialSolution.derive(state.solution, unsatisfied, incompatibility)
     {:ok, unsatisfied.package_range.name, %{state | solution: solution}}
@@ -146,7 +147,7 @@ defmodule HexSolver.Solver do
               state.solution
             else
               package_range = %PackageRange{package_range | constraint: version}
-              Logger.debug("RESOLVER: selecting #{package_range}")
+              Logger.debug("RESOLVER: selecting #{PackageRange.to_string(package_range)}")
               PartialSolution.decide(state.solution, package_range)
             end
 
@@ -164,7 +165,7 @@ defmodule HexSolver.Solver do
   end
 
   defp add_incompatibility(state, incompatibility) do
-    Logger.debug("RESOLVER: fact #{incompatibility}")
+    Logger.debug("RESOLVER: fact #{Incompatibility.to_string(incompatibility)}")
 
     incompatibilities =
       Enum.reduce(incompatibility.terms, state.incompatibilities, fn term, incompatibilities ->
@@ -189,7 +190,7 @@ defmodule HexSolver.Solver do
   # incompatibility that encapsulates the root cause of the conflict and backtracks
   # until the new incompatibility will allow propagation to deduce new assignments.
   defp conflict_resolution(state, incompatibility) do
-    Logger.debug("RESOLVER: conflict #{incompatibility}")
+    Logger.debug("RESOLVER: conflict #{Incompatibility.to_string(incompatibility)}")
     do_conflict_resolution(state, incompatibility, false)
   catch
     :throw, {__MODULE__, :conflict_resolution, incompatibility, state} ->
@@ -319,9 +320,9 @@ defmodule HexSolver.Solver do
 
       Logger.debug("""
       RESOLVER: conflict resolution
-        #{resolution.most_recent_term} is#{partially} satisfied by #{resolution.most_recent_satisfier}
-        which is caused by #{resolution.most_recent_satisfier.cause}
-        thus #{incompatibility}\
+        #{Term.to_string(resolution.most_recent_term)} is#{partially} satisfied by #{Assignment.to_string(resolution.most_recent_satisfier)}
+        which is caused by #{Incompatibility.to_string(resolution.most_recent_satisfier.cause)}
+        thus #{Incompatibility.to_string(incompatibility)}\
       """)
 
       do_conflict_resolution(state, incompatibility, true)
diff --git a/lib/hex_solver/term.ex b/lib/hex_solver/term.ex
index 9620fc5..ea5e533 100644
--- a/lib/hex_solver/term.ex
+++ b/lib/hex_solver/term.ex
@@ -122,7 +122,7 @@ defmodule HexSolver.Term do
   end
 
   def to_string(%Term{package_range: package_range, positive: positive}) do
-    "#{positive(positive)}#{package_range}"
+    "#{positive(positive)}#{PackageRange.to_string(package_range)}"
   end
 
   defp positive(true), do: ""
@@ -137,7 +137,7 @@ defmodule HexSolver.Term do
           %Term{package_range: package_range, positive: positive, optional: optional},
           _opts
         ) do
-      "#Term<#{positive(positive)}#{package_range}#{optional(optional)}>"
+      "#Term<#{positive(positive)}#{PackageRange.to_string(package_range)}#{optional(optional)}>"
     end
 
     defp positive(true), do: ""
diff --git a/test/hex_solver/failure_test.exs b/test/hex_solver/failure_test.exs
index ba0c875..81730d6 100644
--- a/test/hex_solver/failure_test.exs
+++ b/test/hex_solver/failure_test.exs
@@ -118,4 +118,63 @@ defmodule HexSolver.FailureTest do
            So, because "your app" depends on "top2", version solving failed.\
            """
   end
+
+  # Projects consolidate String.Chars without the impls from archives, such as
+  # Hex which vendors the solver, so formatting can't dispatch on solver structs
+  test "formats failures without String.Chars dispatch on solver structs" do
+    Registry.put("foo", "1.0.0", [{"bar", "~> 2.0 or ~> 3.0"}])
+    Registry.put("bar", "1.0.0", [])
+    Registry.put("bar", "2.0.0", [{"baz", "~> 2.0"}])
+    Registry.put("baz", "1.0.0", [])
+
+    dispatched =
+      trace_string_chars(fn ->
+        assert {:error, incompatibility} =
+                 HexSolver.Solver.run(
+                   Registry,
+                   to_dependencies([{"foo", "~> 1.0"}, {"baz", "~> 1.0"}]),
+                   [],
+                   []
+                 )
+
+        Failure.write(incompatibility)
+        Failure.write(incompatibility, ansi: true)
+        inspect(incompatibility)
+      end)
+
+    assert dispatched != []
+    refute Enum.any?(dispatched, &solver_struct?/1)
+  end
+
+  defp trace_string_chars(fun) do
+    tracer = spawn_link(fn -> collect_string_chars([]) end)
+    :erlang.trace_pattern({String.Chars, :to_string, 1}, true, [])
+    :erlang.trace(self(), true, [:call, {:tracer, tracer}])
+
+    try do
+      fun.()
+    after
+      :erlang.trace(self(), false, [:call])
+      :erlang.trace_pattern({String.Chars, :to_string, 1}, false, [])
+    end
+
+    ref = :erlang.trace_delivered(self())
+    assert_receive {:trace_delivered, _pid, ^ref}
+    send(tracer, {:values, self()})
+    assert_receive {:values, values}
+    values
+  end
+
+  defp collect_string_chars(values) do
+    receive do
+      {:trace, _pid, :call, {String.Chars, :to_string, [value]}} ->
+        collect_string_chars([value | values])
+
+      {:values, pid} ->
+        send(pid, {:values, values})
+    end
+  end
+
+  defp solver_struct?(%module{}), do: String.starts_with?(inspect(module), "HexSolver.")
+  defp solver_struct?(_value), do: false
 end