diff --git a/libnetwork/ipams/defaultipam/address_space.go b/libnetwork/ipams/defaultipam/address_space.go
index d305d02ad4..92f886dcc9 100644
--- a/libnetwork/ipams/defaultipam/address_space.go
+++ b/libnetwork/ipams/defaultipam/address_space.go
@@ -2,7 +2,6 @@ package defaultipam
 
 import (
 	"context"
-	"errors"
 	"net/netip"
 	"slices"
 	"sync"
@@ -31,14 +30,6 @@ type addrSpace struct {
 }
 
 func newAddrSpace(predefined []*ipamutils.NetworkToSplit) (*addrSpace, error) {
-	for i, p := range predefined {
-		if !p.Base.IsValid() {
-			return nil, errors.New("newAddrSpace: prefix zero found")
-		}
-
-		predefined[i].Base = p.Base.Masked()
-	}
-
 	slices.SortFunc(predefined, func(a, b *ipamutils.NetworkToSplit) int {
 		return netiputil.PrefixCompare(a.Base, b.Base)
 	})
diff --git a/libnetwork/ipams/defaultipam/allocator.go b/libnetwork/ipams/defaultipam/allocator.go
index 1d2fcf30ee..645f1dfa8a 100644
--- a/libnetwork/ipams/defaultipam/allocator.go
+++ b/libnetwork/ipams/defaultipam/allocator.go
@@ -96,6 +96,8 @@ func splitByIPFamily(s []*ipamutils.NetworkToSplit) ([]*ipamutils.NetworkToSplit
 			return []*ipamutils.NetworkToSplit{}, []*ipamutils.NetworkToSplit{}, fmt.Errorf("network at index %d (%v) is not in canonical form", i, n)
 		}
 
+		n.Base, _ = n.Base.Addr().Unmap().Prefix(n.Base.Bits())
+
 		if n.Base.Addr().Is4() {
 			v4 = append(v4, n)
 		} else {