diff --git a/src/StrEnum.Npgsql.EntityFrameworkCore/ModelBuilderExtensions.cs b/src/StrEnum.Npgsql.EntityFrameworkCore/ModelBuilderExtensions.cs
index b3250c3..7fa4c42 100644
--- a/src/StrEnum.Npgsql.EntityFrameworkCore/ModelBuilderExtensions.cs
+++ b/src/StrEnum.Npgsql.EntityFrameworkCore/ModelBuilderExtensions.cs
@@ -47,18 +47,19 @@ public static ModelBuilder MapStringEnumAsPostgresEnum<TEnum>(this ModelBuilder
 
         foreach (var entityType in modelBuilder.Model.GetEntityTypes())
         {
-            if (entityType.ClrType is null)
-                continue;
-
-            var entityBuilder = modelBuilder.Entity(entityType.ClrType);
-
             foreach (var property in entityType.GetProperties())
             {
                 if (property.ClrType != typeof(TEnum))
                     continue;
 
-                // No HasConversion — see PropertyBuilderExtensions.HasPostgresStringEnum for why.
-                entityBuilder.Property(property.Name).HasColumnType(columnType);
+                // Mutate IMutableProperty directly instead of going through modelBuilder.Entity(...).Property(...).
+                // The latter re-enters EF's entity-discovery conventions, which will probe every CLR property
+                // on the entity (and on any reference-typed nested types they pull in). For an entity whose
+                // complex-collection element exposes e.g. Dictionary<K, V> with a user-supplied HasConversion,
+                // that probing fires before the user's fluent config has been applied — and EF then throws
+                // "Unable to determine the relationship represented by navigation ...". No HasConversion call
+                // here either — see PropertyBuilderExtensions.HasPostgresStringEnum for why.
+                property.SetColumnType(columnType);
             }
         }
 
diff --git a/test/StrEnum.Npgsql.EntityFrameworkCore.UnitTests/ModelBuilderExtensionsTests.cs b/test/StrEnum.Npgsql.EntityFrameworkCore.UnitTests/ModelBuilderExtensionsTests.cs
index 57adbad..b4df357 100644
--- a/test/StrEnum.Npgsql.EntityFrameworkCore.UnitTests/ModelBuilderExtensionsTests.cs
+++ b/test/StrEnum.Npgsql.EntityFrameworkCore.UnitTests/ModelBuilderExtensionsTests.cs
@@ -2,6 +2,7 @@
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
 using Xunit;
 
 namespace StrEnum.Npgsql.EntityFrameworkCore.UnitTests;
@@ -94,4 +95,72 @@ public void MapStringEnumAsPostgresEnum_QualifiesColumnTypeWithSchema()
 
         sportProperty.GetColumnType().Should().Be("races.sport");
     }
+
+    public class Stage
+    {
+        public Dictionary<int, long>? Splits { get; set; }
+    }
+
+    public class Schedule
+    {
+        public List<Stage> Stages { get; set; } = new();
+    }
+
+    public class Tournament
+    {
+        public Guid Id { get; set; }
+        public Schedule Schedule { get; set; } = new();
+        public Sport Sport { get; set; } = null!;
+    }
+
+    private sealed class DictionaryToStringConverter : ValueConverter<Dictionary<int, long>?, string>
+    {
+        public DictionaryToStringConverter()
+            : base(d => "", s => new Dictionary<int, long>())
+        {
+        }
+    }
+
+    private sealed class TournamentContext : DbContext
+    {
+        public DbSet<Tournament> Tournaments => Set<Tournament>();
+
+        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+        {
+            optionsBuilder
+                .UseNpgsql("Host=localhost;Database=tests")
+                .UseStringEnums()
+                .ReplaceService<IModelCacheKeyFactory, UncachedModelKeyFactory>();
+        }
+
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            // Walker call FIRST, before the entity is configured — matches the failing consumer order.
+            modelBuilder.MapStringEnumAsPostgresEnum<Sport>();
+
+            modelBuilder.Entity<Tournament>(t =>
+            {
+                t.ComplexProperty(x => x.Schedule, schedule =>
+                {
+                    schedule.ToJson("schedule");
+                    schedule.ComplexCollection(s => s.Stages, stage =>
+                    {
+                        stage.Property(s => s.Splits).HasConversion(new DictionaryToStringConverter());
+                    });
+                });
+            });
+        }
+
+        public IModel DesignTimeModel => this.GetService<IDesignTimeModel>().Model;
+    }
+
+    [Fact]
+    public void MapStringEnumAsPostgresEnum_DoesNotProbeCustomConvertedComplexCollectionProperties()
+    {
+        using var context = new TournamentContext();
+
+        var act = () => context.DesignTimeModel;
+
+        act.Should().NotThrow();
+    }
 }