diff --git a/src/StatsModels.jl b/src/StatsModels.jl
index 02ac635a..642534c8 100644
--- a/src/StatsModels.jl
+++ b/src/StatsModels.jl
@@ -59,8 +59,8 @@ export
 include("traits.jl")
 include("contrasts.jl")
 include("terms.jl")
-include("temporal_terms.jl")
 include("schema.jl")
+include("temporal_terms.jl")
 include("formula.jl")
 include("modelframe.jl")
 include("statsmodel.jl")
diff --git a/src/temporal_terms.jl b/src/temporal_terms.jl
index 41611bdb..5a29ee24 100644
--- a/src/temporal_terms.jl
+++ b/src/temporal_terms.jl
@@ -26,7 +26,7 @@ struct LeadLagTerm{T<:AbstractTerm, F<:Union{typeof(lead), typeof(lag)}} <: Abst
     nsteps::Int
 end
 
-function apply_schema(t::FunctionTerm{F}, sch, ctx::Type) where F<:Union{typeof(lead), typeof(lag)}
+function apply_schema(t::FunctionTerm{F}, sch::Schema, ctx::Type) where F<:Union{typeof(lead), typeof(lag)}
     opname = string(nameof(F.instance))
     if length(t.args_parsed) == 1  # lag(term)
         term_parsed = first(t.args_parsed)
diff --git a/test/ambiguity.jl b/test/ambiguity.jl
new file mode 100644
index 00000000..de9f10b8
--- /dev/null
+++ b/test/ambiguity.jl
@@ -0,0 +1,3 @@
+@testset "Ambiguity detection" begin
+    @test isempty(Test.detect_ambiguities(StatsModels))
+end
diff --git a/test/extension.jl b/test/extension.jl
index 10a56483..2f056928 100644
--- a/test/extension.jl
+++ b/test/extension.jl
@@ -93,4 +93,9 @@ end
     @testset "Fallback" begin
         @test_throws ArgumentError modelcols(DummyTerm(), (a=[1], ))
     end
+
+    @testset "Ambiguity detection" begin
+        # ambiguities are introduced by adding additional methods here
+        @test_broken isempty(Test.detect_ambiguities(StatsModels))
+    end
 end
diff --git a/test/runtests.jl b/test/runtests.jl
index 02713f1d..a39e0777 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -8,7 +8,8 @@ using StatsBase
 
 using StatsModels: ContrastsMatrix
 
-my_tests = ["formula.jl",
+my_tests = ["ambiguity.jl",
+            "formula.jl",
             "terms.jl",
             "temporal_terms.jl",
             "schema.jl",