diff --git a/base/array.jl b/base/array.jl
index a8256ec8ff99a..f13c6ee08358e 100644
--- a/base/array.jl
+++ b/base/array.jl
@@ -512,10 +512,12 @@ function _collect(::Type{T}, itr, isz::SizeUnknown) where T
 end
 
 # make a collection similar to `c` and appropriate for collecting `itr`
-_similar_for(c::AbstractArray, T, itr, ::SizeUnknown) = similar(c, T, 0)
-_similar_for(c::AbstractArray, T, itr, ::HasLength) = similar(c, T, Int(length(itr)::Integer))
-_similar_for(c::AbstractArray, T, itr, ::HasShape) = similar(c, T, axes(itr))
-_similar_for(c, T, itr, isz) = similar(c, T)
+_similar_for(c::AbstractArray, ::Type{T}, itr, ::SizeUnknown) where {T} = similar(c, T, 0)
+_similar_for(c::AbstractArray, ::Type{T}, itr, ::HasLength) where {T} =
+    similar(c, T, Int(length(itr)::Integer))
+_similar_for(c::AbstractArray, ::Type{T}, itr, ::HasShape) where {T} =
+    similar(c, T, axes(itr))
+_similar_for(c, ::Type{T}, itr, isz) where {T} = similar(c, T)
 
 """
     collect(collection)
diff --git a/base/dict.jl b/base/dict.jl
index 3f52110e8b8f9..fb27cc10cc04d 100644
--- a/base/dict.jl
+++ b/base/dict.jl
@@ -760,4 +760,5 @@ isempty(t::ImmutableDict) = !isdefined(t, :parent)
 empty(::ImmutableDict, ::Type{K}, ::Type{V}) where {K, V} = ImmutableDict{K,V}()
 
 _similar_for(c::Dict, ::Type{Pair{K,V}}, itr, isz) where {K, V} = empty(c, K, V)
-_similar_for(c::AbstractDict, T, itr, isz) = throw(ArgumentError("for AbstractDicts, similar requires an element type of Pair;\n  if calling map, consider a comprehension instead"))
+_similar_for(c::AbstractDict, ::Type{T}, itr, isz) where {T} =
+    throw(ArgumentError("for AbstractDicts, similar requires an element type of Pair;\n  if calling map, consider a comprehension instead"))
diff --git a/base/set.jl b/base/set.jl
index c53c50610c40f..0ed73407ca6b1 100644
--- a/base/set.jl
+++ b/base/set.jl
@@ -34,7 +34,7 @@ empty(s::AbstractSet{T}, ::Type{U}=T) where {T,U} = Set{U}()
 # by default, a Set is returned
 emptymutable(s::AbstractSet{T}, ::Type{U}=T) where {T,U} = Set{U}()
 
-_similar_for(c::AbstractSet, T, itr, isz) = empty(c, T)
+_similar_for(c::AbstractSet, ::Type{T}, itr, isz) where {T} = empty(c, T)
 
 function show(io::IO, s::Set)
     print(io, "Set(")