diff --git a/.changelog/bf2d083eb544421e9c0542e73951e635.json b/.changelog/bf2d083eb544421e9c0542e73951e635.json
new file mode 100644
index 00000000..e2c4f0a9
--- /dev/null
+++ b/.changelog/bf2d083eb544421e9c0542e73951e635.json
@@ -0,0 +1,8 @@
+{
+    "id": "bf2d083e-b544-421e-9c05-42e73951e635",
+    "type": "bugfix",
+    "description": "Adjust the initial sizes of each middleware phase to avoid some unnecessary reallocation.",
+    "modules": [
+        "."
+    ]
+}
\ No newline at end of file
diff --git a/middleware/ordered_group.go b/middleware/ordered_group.go
index 4b195308..daf90136 100644
--- a/middleware/ordered_group.go
+++ b/middleware/ordered_group.go
@@ -23,12 +23,14 @@ type orderedIDs struct {
 	items map[string]ider
 }
 
-const baseOrderedItems = 5
+// selected based on the general upper bound of # of middlewares in each step
+// in the downstream aws-sdk-go-v2
+const baseOrderedItems = 8
 
-func newOrderedIDs() *orderedIDs {
+func newOrderedIDs(cap int) *orderedIDs {
 	return &orderedIDs{
-		order: newRelativeOrder(),
-		items: make(map[string]ider, baseOrderedItems),
+		order: newRelativeOrder(cap),
+		items: make(map[string]ider, cap),
 	}
 }
 
@@ -141,9 +143,9 @@ type relativeOrder struct {
 	order []string
 }
 
-func newRelativeOrder() *relativeOrder {
+func newRelativeOrder(cap int) *relativeOrder {
 	return &relativeOrder{
-		order: make([]string, 0, baseOrderedItems),
+		order: make([]string, 0, cap),
 	}
 }
 
diff --git a/middleware/ordered_group_test.go b/middleware/ordered_group_test.go
index 3c6f6a02..d0c7a77b 100644
--- a/middleware/ordered_group_test.go
+++ b/middleware/ordered_group_test.go
@@ -6,7 +6,7 @@ import (
 )
 
 func TestOrderedIDsAdd(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 
 	noError(t, o.Add(&mockIder{"first"}, After))
 	noError(t, o.Add(&mockIder{"second"}, After))
@@ -31,7 +31,7 @@ func TestOrderedIDsAdd(t *testing.T) {
 }
 
 func TestOrderedIDsInsert(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 
 	noError(t, o.Add(&mockIder{"first"}, After))
 	noError(t, o.Insert(&mockIder{"third"}, "first", After))
@@ -63,7 +63,7 @@ func TestOrderedIDsInsert(t *testing.T) {
 }
 
 func TestOrderedIDsGet(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 
 	noError(t, o.Add(&mockIder{"first"}, After))
 	noError(t, o.Add(&mockIder{"second"}, After))
@@ -83,7 +83,7 @@ func TestOrderedIDsGet(t *testing.T) {
 }
 
 func TestOrderedIDsSwap(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 
 	noError(t, o.Add(&mockIder{"first"}, After))
 	noError(t, o.Add(&mockIder{"second"}, After))
@@ -119,7 +119,7 @@ func TestOrderedIDsSwap(t *testing.T) {
 }
 
 func TestOrderedIDsRemove(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 	firstIder := &mockIder{"first"}
 	noError(t, o.Add(firstIder, After))
 	noError(t, o.Insert(&mockIder{"third"}, "first", After))
@@ -144,7 +144,7 @@ func TestOrderedIDsRemove(t *testing.T) {
 }
 
 func TestOrderedIDsClear(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 
 	noError(t, o.Add(&mockIder{"first"}, After))
 	noError(t, o.Add(&mockIder{"second"}, After))
@@ -161,7 +161,7 @@ func TestOrderedIDsClear(t *testing.T) {
 }
 
 func TestOrderedIDsGetOrder(t *testing.T) {
-	o := newOrderedIDs()
+	o := newOrderedIDs(10)
 
 	noError(t, o.Add(&mockIder{"first"}, After))
 	noError(t, o.Add(&mockIder{"second"}, After))
diff --git a/middleware/step_build.go b/middleware/step_build.go
index 7e1d94ca..cc7fe89c 100644
--- a/middleware/step_build.go
+++ b/middleware/step_build.go
@@ -79,7 +79,7 @@ type BuildStep struct {
 // initialization added to it.
 func NewBuildStep() *BuildStep {
 	return &BuildStep{
-		ids: newOrderedIDs(),
+		ids: newOrderedIDs(baseOrderedItems),
 	}
 }
 
diff --git a/middleware/step_deserialize.go b/middleware/step_deserialize.go
index 44860721..9a6679a5 100644
--- a/middleware/step_deserialize.go
+++ b/middleware/step_deserialize.go
@@ -85,7 +85,8 @@ type DeserializeStep struct {
 // initialization added to it.
 func NewDeserializeStep() *DeserializeStep {
 	return &DeserializeStep{
-		ids: newOrderedIDs(),
+		// downstream SDK typically has larger Deserialize step
+		ids: newOrderedIDs(baseOrderedItems * 2),
 	}
 }
 
diff --git a/middleware/step_finalize.go b/middleware/step_finalize.go
index 065e3885..76eab249 100644
--- a/middleware/step_finalize.go
+++ b/middleware/step_finalize.go
@@ -79,7 +79,8 @@ type FinalizeStep struct {
 // initialization added to it.
 func NewFinalizeStep() *FinalizeStep {
 	return &FinalizeStep{
-		ids: newOrderedIDs(),
+		// downstream SDK typically has larger Finalize step
+		ids: newOrderedIDs(baseOrderedItems * 2),
 	}
 }
 
diff --git a/middleware/step_initialize.go b/middleware/step_initialize.go
index fe359144..312be3a3 100644
--- a/middleware/step_initialize.go
+++ b/middleware/step_initialize.go
@@ -79,7 +79,7 @@ type InitializeStep struct {
 // initialization added to it.
 func NewInitializeStep() *InitializeStep {
 	return &InitializeStep{
-		ids: newOrderedIDs(),
+		ids: newOrderedIDs(baseOrderedItems),
 	}
 }
 
diff --git a/middleware/step_serialize.go b/middleware/step_serialize.go
index 114bafce..a4ce4bee 100644
--- a/middleware/step_serialize.go
+++ b/middleware/step_serialize.go
@@ -85,7 +85,7 @@ type SerializeStep struct {
 // serialize the input parameters into.
 func NewSerializeStep(newRequest func() interface{}) *SerializeStep {
 	return &SerializeStep{
-		ids:        newOrderedIDs(),
+		ids:        newOrderedIDs(baseOrderedItems),
 		newRequest: newRequest,
 	}
 }