diff --git a/base/array.jl b/base/array.jl
index 5c9b37f887ea8..61a3c39ca2bb7 100644
--- a/base/array.jl
+++ b/base/array.jl
@@ -993,7 +993,7 @@ function setindex!(A::Array{T}, x, i::Int) where {T}
 end
 function _setindex!(A::Array{T}, x::T, i::Int) where {T}
     @_noub_if_noinbounds_meta
-    @boundscheck (i - 1)%UInt < length(A)%UInt || throw_boundserror(A, (i,))
+    @boundscheck checkbounds(Bool, A, i) || throw_boundserror(A, (i,))
     memoryrefset!(memoryrefnew(A.ref, i, false), x, :not_atomic, false)
     return A
 end
diff --git a/base/essentials.jl b/base/essentials.jl
index 820cce6839f13..e1bc648e7dbd0 100644
--- a/base/essentials.jl
+++ b/base/essentials.jl
@@ -377,13 +377,14 @@ macro _nospecializeinfer_meta()
     return Expr(:meta, :nospecializeinfer)
 end
 
-function _checkbounds_array(::Type{Bool}, A::Union{Array, GenericMemory}, i::Int)
+# These special checkbounds methods are defined early for bootstrapping
+function checkbounds(::Type{Bool}, A::Union{Array, Memory}, i::Int)
     @inline
     ult_int(bitcast(UInt, sub_int(i, 1)), bitcast(UInt, length(A)))
 end
-function _checkbounds_array(A::Union{Array, GenericMemory}, i::Int)
+function checkbounds(A::Union{Array, GenericMemory}, i::Int)
     @inline
-    _checkbounds_array(Bool, A, i) || throw_boundserror(A, (i,))
+    checkbounds(Bool, A, i) || throw_boundserror(A, (i,))
 end
 
 default_access_order(a::GenericMemory{:not_atomic}) = :not_atomic
@@ -393,7 +394,7 @@ default_access_order(a::GenericMemoryRef{:atomic}) = :monotonic
 
 function getindex(A::GenericMemory, i::Int)
     @_noub_if_noinbounds_meta
-    (@_boundscheck) && _checkbounds_array(A, i)
+    (@_boundscheck) && checkbounds(A, i)
     memoryrefget(memoryrefnew(memoryrefnew(A), i, false), default_access_order(A), false)
 end
 
@@ -962,13 +963,13 @@ end
 # linear indexing
 function getindex(A::Array, i::Int)
     @_noub_if_noinbounds_meta
-    @boundscheck _checkbounds_array(A, i)
+    @boundscheck checkbounds(A, i)
     memoryrefget(memoryrefnew(getfield(A, :ref), i, false), :not_atomic, false)
 end
 # simple Array{Any} operations needed for bootstrap
 function setindex!(A::Array{Any}, @nospecialize(x), i::Int)
     @_noub_if_noinbounds_meta
-    @boundscheck _checkbounds_array(A, i)
+    @boundscheck checkbounds(A, i)
     memoryrefset!(memoryrefnew(getfield(A, :ref), i, false), x, :not_atomic, false)
     return A
 end
diff --git a/base/genericmemory.jl b/base/genericmemory.jl
index 1b45ba23bcded..d25d213a3546e 100644
--- a/base/genericmemory.jl
+++ b/base/genericmemory.jl
@@ -106,7 +106,7 @@ sizeof(a::GenericMemory) = Core.sizeof(a)
 # multi arg case will be overwritten later. This is needed for bootstrapping
 function isassigned(a::GenericMemory, i::Int)
     @inline
-    @boundscheck (i - 1)%UInt < length(a)%UInt || return false
+    @boundscheck checkbounds(Bool, a, i) || return false
     return @inbounds memoryref_isassigned(memoryref(a, i), default_access_order(a), false)
 end
 
@@ -227,7 +227,7 @@ Memory{T}(x::AbstractArray{S,1}) where {T,S} = copyto_axcheck!(Memory{T}(undef,
 
 function _iterate_array(A::Union{Memory, Array}, i::Int)
     @inline
-    (i - 1)%UInt < length(A)%UInt ? (A[i], i + 1) : nothing
+    checkbounds(Bool, A, i) ? (A[i], i + 1) : nothing
 end
 
 iterate(A::Memory, i=1) = (@inline; _iterate_array(A, i))
diff --git a/base/strings/basic.jl b/base/strings/basic.jl
index 314903898b92a..6619a2b25574e 100644
--- a/base/strings/basic.jl
+++ b/base/strings/basic.jl
@@ -797,7 +797,7 @@ size(s::CodeUnits) = (length(s),)
 elsize(s::Type{<:CodeUnits{T}}) where {T} = sizeof(T)
 @propagate_inbounds getindex(s::CodeUnits, i::Int) = codeunit(s.s, i)
 IndexStyle(::Type{<:CodeUnits}) = IndexLinear()
-@inline iterate(s::CodeUnits, i=1) = (i % UInt) - 1 < length(s) ? (@inbounds s[i], i + 1) : nothing
+@inline iterate(s::CodeUnits, i=1) = checkbounds(Bool, s, i) ? (@inbounds s[i], i + 1) : nothing
 
 
 write(io::IO, s::CodeUnits) = write(io, s.s)