diff --git a/base/iddict.jl b/base/iddict.jl
index 7247a85c9afc8..dc7af461b09ec 100644
--- a/base/iddict.jl
+++ b/base/iddict.jl
@@ -68,7 +68,7 @@ end
 
 empty(d::IdDict, ::Type{K}, ::Type{V}) where {K, V} = IdDict{K,V}()
 
-function rehash!(d::IdDict, newsz = length(d.ht))
+function rehash!(d::IdDict, newsz = length(d.ht)%UInt)
     d.ht = ccall(:jl_idtable_rehash, Vector{Any}, (Any, Csize_t), d.ht, newsz)
     d
 end
@@ -89,7 +89,7 @@ function setindex!(d::IdDict{K,V}, @nospecialize(val), @nospecialize(key)) where
         val = convert(V, val)
     end
     if d.ndel >= ((3*length(d.ht))>>2)
-        rehash!(d, max(length(d.ht)>>1, 32))
+        rehash!(d, max((length(d.ht)%UInt)>>1, 32))
         d.ndel = 0
     end
     inserted = RefValue{Cint}(0)
@@ -143,7 +143,7 @@ end
 _oidd_nextind(a, i) = reinterpret(Int, ccall(:jl_eqtable_nextind, Csize_t, (Any, Csize_t), a, i))
 
 function iterate(d::IdDict{K,V}, idx=0) where {K, V}
-    idx = _oidd_nextind(d.ht, idx)
+    idx = _oidd_nextind(d.ht, idx%UInt)
     idx == -1 && return nothing
     return (Pair{K, V}(d.ht[idx + 1]::K, d.ht[idx + 2]::V), idx + 2)
 end