diff --git a/base/compiler/ssair/passes.jl b/base/compiler/ssair/passes.jl
index d1dfad473726b..d3519ff487e2e 100644
--- a/base/compiler/ssair/passes.jl
+++ b/base/compiler/ssair/passes.jl
@@ -178,7 +178,7 @@ function walk_to_defs(compact::IncrementalCompact, @nospecialize(defssa), @nospe
     found_def = false
     ## Track which PhiNodes, SSAValue intermediaries
     ## we forwarded through.
-    visited = IdSet{Any}()
+    visited = IdDict{Any, Any}()
     worklist_defs = Any[]
     worklist_constraints = Any[]
     leaves = Any[]
@@ -187,7 +187,7 @@ function walk_to_defs(compact::IncrementalCompact, @nospecialize(defssa), @nospe
     while !isempty(worklist_defs)
         defssa = pop!(worklist_defs)
         typeconstraint = pop!(worklist_constraints)
-        push!(visited, defssa)
+        visited[defssa] = typeconstraint
         def = compact[defssa]
         if isa(def, PhiNode)
             push!(visited_phinodes, defssa)
@@ -211,9 +211,15 @@ function walk_to_defs(compact::IncrementalCompact, @nospecialize(defssa), @nospe
                 if isa(val, AnySSAValue)
                     new_def, new_constraint = simple_walk_constraint(compact, val, typeconstraint)
                     if isa(new_def, AnySSAValue)
-                        if !(new_def in visited)
+                        if !haskey(visited, new_def)
                             push!(worklist_defs, new_def)
                             push!(worklist_constraints, new_constraint)
+                        elseif !(new_constraint <: visited[new_def])
+                            # We have reached the same definition via a different
+                            # path, with a different type constraint. We may have
+                            # to redo some work here with the wider typeconstraint
+                            push!(worklist_defs, new_def)
+                            push!(worklist_constraints, tmerge(new_constraint, visited[new_def]))
                         end
                         continue
                     end
diff --git a/test/compiler/ssair.jl b/test/compiler/ssair.jl
index 88ce5985a23ac..7603e7b8a0574 100644
--- a/test/compiler/ssair.jl
+++ b/test/compiler/ssair.jl
@@ -96,3 +96,23 @@ let
         Meta.isexpr(ex, :meta)
     end
 end
+
+# Issue #32579 - Optimizer bug involving type constraints
+function f32579(x::Int, b::Bool)
+    if b
+        x = nothing
+    end
+    if isa(x, Int)
+        y = x
+    else
+        y = x
+    end
+    if isa(y, Nothing)
+        z = y
+    else
+        z = y
+    end
+    return z === nothing
+end
+@test f32579(0, true) === true
+@test f32579(0, false) === false