diff --git a/src/Framework/Framework/Compilation/Directives/PropertyDeclarationDirectiveCompiler.cs b/src/Framework/Framework/Compilation/Directives/PropertyDeclarationDirectiveCompiler.cs
index e9405be5dc..4131d51b1e 100644
--- a/src/Framework/Framework/Compilation/Directives/PropertyDeclarationDirectiveCompiler.cs
+++ b/src/Framework/Framework/Compilation/Directives/PropertyDeclarationDirectiveCompiler.cs
@@ -159,8 +159,10 @@ ImmutableList<IAbstractPropertyDeclarationDirective> propertyDirectives
                     baseType.FullName + "||" + string.Join("|", imports) + "||" + string.Join("|", properties)
                 )
             );
-            var hash = Convert.ToBase64String(hashBytes, 0, 16);
-
+            var hash = Convert.ToBase64String(hashBytes, 0, 16)
+                .Replace('+', '_')
+                .Replace('/', '_')
+                .TrimEnd('=');
             var typeName = "DotvvmMarkupControl-" + hash;
 
             return GetOrCreateDynamicType(baseType, typeName, propertyDirectives);
diff --git a/src/Framework/Framework/Compilation/Directives/ResolvedPropertyDeclarationDirectiveCompiler.cs b/src/Framework/Framework/Compilation/Directives/ResolvedPropertyDeclarationDirectiveCompiler.cs
index 97e66aeb88..c94b125f87 100644
--- a/src/Framework/Framework/Compilation/Directives/ResolvedPropertyDeclarationDirectiveCompiler.cs
+++ b/src/Framework/Framework/Compilation/Directives/ResolvedPropertyDeclarationDirectiveCompiler.cs
@@ -12,6 +12,7 @@ namespace DotVVM.Framework.Compilation.Directives
     public class ResolvedPropertyDeclarationDirectiveCompiler : PropertyDeclarationDirectiveCompiler
     {
         private static readonly Lazy<ModuleBuilder> DynamicMarkupControlAssembly = new(CreateDynamicMarkupControlAssembly);
+        private static readonly object locker = new();
 
         public ResolvedPropertyDeclarationDirectiveCompiler(
             ImmutableDictionary<string, ImmutableList<DothtmlDirectiveNode>> directiveNodesByName,
@@ -45,18 +46,29 @@ protected override IPropertyDescriptor TryCreateDotvvmPropertyFromDirective(IAbs
             string typeName,
             ImmutableList<IAbstractPropertyDeclarationDirective> propertyDirectives)
         {
-            if (DynamicMarkupControlAssembly.Value.GetType(typeName) is { } type)
+            // this must be done in the lock, otherwise the DynamicMarkupControlAssembly can return TypeBuilder instead of fully-built System.Type
+            lock (locker)
             {
-                return new ResolvedTypeDescriptor(type);
-            }
+                if (DynamicMarkupControlAssembly.Value.GetType(typeName) is { } type)
+                {
+                    return new ResolvedTypeDescriptor(type);
+                }
 
-            var declaringTypeBuilder =
-                DynamicMarkupControlAssembly.Value.DefineType(typeName, TypeAttributes.Public, ResolvedTypeDescriptor.ToSystemType(baseType));
-            var createdTypeInfo = declaringTypeBuilder.CreateTypeInfo()?.AsType();
+                try
+                {
+                    var declaringTypeBuilder =
+                        DynamicMarkupControlAssembly.Value.DefineType(typeName, TypeAttributes.Public, ResolvedTypeDescriptor.ToSystemType(baseType));
+                    var createdTypeInfo = declaringTypeBuilder.CreateTypeInfo()?.AsType();
 
-            return createdTypeInfo is not null
-                ? new ResolvedTypeDescriptor(createdTypeInfo)
-                : null;
+                    return createdTypeInfo is not null
+                        ? new ResolvedTypeDescriptor(createdTypeInfo)
+                        : null;
+                }
+                catch (Exception ex)
+                {
+                    throw new InvalidOperationException($"Failed to create dynamic type '{typeName}'", ex);
+                }
+            }
         }
 
         private static ModuleBuilder CreateDynamicMarkupControlAssembly()
diff --git a/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-client.html b/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-client.html
index 045eb23e48..06c8ef08cb 100644
--- a/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-client.html
+++ b/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-client.html
@@ -7,7 +7,7 @@
     <!-- Resource c7-item of type TemplateResource. -->
     <template id=c7-item><!-- ko with: $item -->
             <!-- ko with: $rawData --><div>
-            <input type=button onclick='dotvvm.postBack(this,["HItems/[$indexPath]","$parent"],"RR93KduwUKJIXxFp","c7"+&#39;_&#39;+(ko.contextFor(this).$parentContext.$indexPath.map(ko.unwrap).join("_")+"L")+&#39;_&#39;+"c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' data-bind="value: Label" /></div><!-- /ko -->
+            <input type=button onclick='dotvvm.postBack(this,["HItems/[$indexPath]","$parent"],"bu4IebQeKpjPj6ST","c7"+&#39;_&#39;+(ko.contextFor(this).$parentContext.$indexPath.map(ko.unwrap).join("_")+"L")+&#39;_&#39;+"c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' data-bind="value: Label" /></div><!-- /ko -->
         <!-- /ko --><!-- ko template: { foreach: $item().Children, name: "c7-item", hierarchyRole: "Child" } --><!-- ko if: Children()?.length --><!-- /ko --><!-- /ko --></template>
 
 </body>
diff --git a/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-server.html b/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-server.html
index c37b3bba11..35facebde8 100644
--- a/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-server.html
+++ b/src/Tests/ControlTests/testoutputs/HierarchyRepeaterTests.CommandInMarkupControl-server.html
@@ -4,19 +4,19 @@
 
     <div><!-- ko dotvvm-SSR-foreach: { data: HItems } --><!-- ko dotvvm-SSR-item: 0 -->
             <!-- ko with: $rawData --><div>
-            <input type=button value=A onclick='dotvvm.postBack(this,["HItems/[0]","$parent"],"RR93KduwUKJIXxFp","c7_0L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
+            <input type=button value=A onclick='dotvvm.postBack(this,["HItems/[0]","$parent"],"bu4IebQeKpjPj6ST","c7_0L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
         <!-- /ko --><!-- ko dotvvm-SSR-foreach: { data: ko.unwrap($foreachCollectionSymbol)[0]().Children } --><!-- ko dotvvm-SSR-item: 0 -->
             <!-- ko with: $rawData --><div>
-            <input type=button value=A_1 onclick='dotvvm.postBack(this,["HItems/[0]/[0]","$parent"],"RR93KduwUKJIXxFp","c7_0_0L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
+            <input type=button value=A_1 onclick='dotvvm.postBack(this,["HItems/[0]/[0]","$parent"],"bu4IebQeKpjPj6ST","c7_0_0L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
         <!-- /ko --><!-- ko dotvvm-SSR-foreach: { data: ko.unwrap($foreachCollectionSymbol)[0]().Children } --><!-- ko dotvvm-SSR-item: 0 -->
             <!-- ko with: $rawData --><div>
-            <input type=button value=A_1_1 onclick='dotvvm.postBack(this,["HItems/[0]/[0]/[0]","$parent"],"RR93KduwUKJIXxFp","c7_0_0_0L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
+            <input type=button value=A_1_1 onclick='dotvvm.postBack(this,["HItems/[0]/[0]/[0]","$parent"],"bu4IebQeKpjPj6ST","c7_0_0_0L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
         <!-- /ko --><!-- ko dotvvm-SSR-item: 1 -->
             <!-- ko with: $rawData --><div>
-            <input type=button value=A_1_2 onclick='dotvvm.postBack(this,["HItems/[0]/[0]/[1]","$parent"],"RR93KduwUKJIXxFp","c7_0_0_1L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
+            <input type=button value=A_1_2 onclick='dotvvm.postBack(this,["HItems/[0]/[0]/[1]","$parent"],"bu4IebQeKpjPj6ST","c7_0_0_1L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
         <!-- /ko --><!-- /ko --><!-- /ko --><!-- ko dotvvm-SSR-item: 1 -->
             <!-- ko with: $rawData --><div>
-            <input type=button value=B onclick='dotvvm.postBack(this,["HItems/[1]","$parent"],"RR93KduwUKJIXxFp","c7_1L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
+            <input type=button value=B onclick='dotvvm.postBack(this,["HItems/[1]","$parent"],"bu4IebQeKpjPj6ST","c7_1L_c9",null,[],[],undefined).catch(dotvvm.log.logPostBackScriptError);event.stopPropagation();return false;' /></div><!-- /ko -->
         <!-- /ko --><!-- /ko --></div>