diff --git a/src/mapreduce.jl b/src/mapreduce.jl
index 9182ee8..ff8180a 100644
--- a/src/mapreduce.jl
+++ b/src/mapreduce.jl
@@ -33,17 +33,17 @@ function Base._mapreduce_dim(f, op, ::NamedTuple{()}, A::StridedView, dims)
 end
 
 function Base.map(
-        f::F, a1::StridedView{<:Any, N},
+        @nospecialize(f), a1::StridedView{<:Any, N},
         A::Vararg{StridedView{<:Any, N}}
-    ) where {F, N}
+    ) where {N}
     T = Base.promote_eltype(a1, A...)
     return map!(f, similar(a1, T), a1, A...)
 end
 
 function Base.map!(
-        f::F, b::StridedView{<:Any, N}, a1::StridedView{<:Any, N},
+        @nospecialize(f), b::StridedView{<:Any, N}, a1::StridedView{<:Any, N},
         A::Vararg{StridedView{<:Any, N}}
-    ) where {F, N}
+    ) where {N}
     dims = size(b)
 
     # Check dimesions
@@ -59,7 +59,7 @@ function Base.map!(
     return b
 end
 
-function _mapreduce(f, op, A::StridedView{T}, nt = nothing) where {T}
+function _mapreduce(@nospecialize(f), @nospecialize(op), A::StridedView{T}, nt = nothing) where {T}
     if isempty(A)
         b = Base.mapreduce_empty(f, op, T)
         return nt === nothing ? b : op(b, nt.init)
@@ -79,7 +79,7 @@ function _mapreduce(f, op, A::StridedView{T}, nt = nothing) where {T}
 end
 
 function Base.mapreducedim!(
-        f, op, b::StridedView{<:Any, N},
+        @nospecialize(f), @nospecialize(op), b::StridedView{<:Any, N},
         a1::StridedView{<:Any, N},
         A::Vararg{StridedView{<:Any, N}}
     ) where {N}
@@ -93,7 +93,7 @@ function Base.mapreducedim!(
 end
 
 function _mapreducedim!(
-        (f), (op), (initop),
+        @nospecialize(f), @nospecialize(op), @nospecialize(initop),
         dims::Dims, arrays::Tuple{Vararg{StridedView}}
     )
     if any(isequal(0), dims)
@@ -107,7 +107,7 @@ function _mapreducedim!(
 end
 
 function _mapreduce_fuse!(
-        (f), (op), (initop),
+        @nospecialize(f), @nospecialize(op), @nospecialize(initop),
         dims::Dims, arrays::Tuple{Vararg{StridedView}}
     )
     # Fuse dimensions if possible: assume that at least one array, e.g. the output array in
@@ -130,7 +130,7 @@ function _mapreduce_fuse!(
 end
 
 function _mapreduce_order!(
-        (f), (op), (initop),
+        @nospecialize(f), @nospecialize(op), @nospecialize(initop),
         dims, strides, arrays
     )
     M = length(arrays)
@@ -155,7 +155,7 @@ end
 
 const MINTHREADLENGTH = 1 << 15 # minimal length before any kind of threading is applied
 function _mapreduce_block!(
-        (f), (op), (initop),
+        @nospecialize(f), @nospecialize(op), @nospecialize(initop),
         dims, strides, offsets, costs, arrays
     )
     bytestrides = map((s, stride) -> s .* stride, sizeof.(eltype.(arrays)), strides)
@@ -214,7 +214,7 @@ end
 # nthreads: number of threads spacing: extra addition to offset of array 1, to account for
 # reduction
 function _mapreduce_threaded!(
-        (f), (op), (initop),
+        @nospecialize(f), @nospecialize(op), @nospecialize(initop),
         dims, blocks, strides, offsets, costs, arrays, nthreads,
         spacing, taskindex
     )
@@ -261,6 +261,10 @@ end
         strides::NTuple{M, NTuple{N, Int}},
         offsets::NTuple{M, Int}
     ) where {N, M}
+    return _mapreduce_kernel_expr(f, op, initop, N, M)
+end
+
+function _mapreduce_kernel_expr(f, op, initop, N::Int, M::Int)
 
     # many variables
     blockloopvars = Array{Symbol}(undef, N)