diff --git a/toolchain/check/convert.cpp b/toolchain/check/convert.cpp
index 155808cfd744..64386c37b7e5 100644
--- a/toolchain/check/convert.cpp
+++ b/toolchain/check/convert.cpp
@@ -392,6 +392,12 @@ static auto ConvertStructToStructOrClass(Context& context,
   auto& sem_ir = context.sem_ir();
   auto src_elem_fields = sem_ir.inst_blocks().Get(src_type.fields_id);
   auto dest_elem_fields = sem_ir.inst_blocks().Get(dest_type.fields_id);
+  bool dest_has_vptr =
+      !dest_elem_fields.empty() &&
+      sem_ir.insts()
+              .GetAs<SemIR::StructTypeField>(dest_elem_fields.front())
+              .name_id == SemIR::NameId::Vptr;
+  auto dest_elem_fields_size = dest_elem_fields.size() - dest_has_vptr;
 
   auto value = sem_ir.insts().Get(value_id);
   auto value_loc_id = sem_ir.insts().GetLocId(value_id);
@@ -411,14 +417,14 @@ static auto ConvertStructToStructOrClass(Context& context,
   // Check that the structs are the same size.
   // TODO: If not, include the name of the first source field that doesn't
   // exist in the destination or vice versa in the diagnostic.
-  if (src_elem_fields.size() != dest_elem_fields.size()) {
+  if (src_elem_fields.size() != dest_elem_fields_size) {
     CARBON_DIAGNOSTIC(
         StructInitElementCountMismatch, Error,
         "cannot initialize {0:class|struct} with {1} field{1:s} from struct "
         "with {2} field{2:s}",
         BoolAsSelect, IntAsSelect, IntAsSelect);
     context.emitter().Emit(value_loc_id, StructInitElementCountMismatch,
-                           ToClass, dest_elem_fields.size(),
+                           ToClass, dest_elem_fields_size,
                            src_elem_fields.size());
     return SemIR::InstId::BuiltinError;
   }
@@ -449,14 +455,19 @@ static auto ConvertStructToStructOrClass(Context& context,
   // of the source.
   // TODO: Annotate diagnostics coming from here with the element index.
   auto new_block =
-      literal_elems_id.is_valid()
+      literal_elems_id.is_valid() && !dest_has_vptr
           ? SemIR::CopyOnWriteInstBlock(sem_ir, literal_elems_id)
           : SemIR::CopyOnWriteInstBlock(
                 sem_ir, SemIR::CopyOnWriteInstBlock::UninitializedBlock{
-                            src_elem_fields.size()});
+                            dest_elem_fields.size()});
   for (auto [i, dest_field_id] : llvm::enumerate(dest_elem_fields)) {
     auto dest_field =
         sem_ir.insts().GetAs<SemIR::StructTypeField>(dest_field_id);
+    if (dest_field.name_id == SemIR::NameId::Vptr) {
+      // TODO: Initialize the vptr to point to a vtable.
+      new_block.Set(i, SemIR::InstId::BuiltinError);
+      continue;
+    }
 
     // Find the matching source field.
     auto src_field_index = i;
diff --git a/toolchain/check/testdata/class/virtual_modifiers.carbon b/toolchain/check/testdata/class/virtual_modifiers.carbon
index 3807b1d08ed3..3cf14070cd5d 100644
--- a/toolchain/check/testdata/class/virtual_modifiers.carbon
+++ b/toolchain/check/testdata/class/virtual_modifiers.carbon
@@ -37,17 +37,13 @@ base class Derived {
   extend base: Modifiers.Base;
 }
 
-// --- fail_todo_init.carbon
+// --- init.carbon
 
 package Init;
 
 import Modifiers;
 
 fn F() {
-  // TODO: The vptr shouldn't be counted for programmer-facing behavior.
-  // CHECK:STDERR: fail_todo_init.carbon:[[@LINE+3]]:27: error: cannot initialize class with 1 field from struct with 0 fields [StructInitElementCountMismatch]
-  // CHECK:STDERR:   var v: Modifiers.Base = {};
-  // CHECK:STDERR:                           ^~
   var v: Modifiers.Base = {};
 }
 
@@ -190,7 +186,7 @@ fn F() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: virtual fn @F();
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- fail_todo_init.carbon
+// CHECK:STDOUT: --- init.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %F.type: type = fn_type @F [template]
@@ -243,8 +239,10 @@ fn F() {
 // CHECK:STDOUT:   %Base.ref: type = name_ref Base, imports.%import_ref.1 [template = constants.%Base]
 // CHECK:STDOUT:   %v.var: ref %Base = var v
 // CHECK:STDOUT:   %v: ref %Base = bind_name v, %v.var
-// CHECK:STDOUT:   %.loc11: %.6 = struct_literal ()
-// CHECK:STDOUT:   assign %v.var, <error>
+// CHECK:STDOUT:   %.loc7_28.1: %.6 = struct_literal ()
+// CHECK:STDOUT:   %.loc7_28.2: init %Base = class_init (<error>), %v.var [template = <error>]
+// CHECK:STDOUT:   %.loc7_29: init %Base = converted %.loc7_28.1, %.loc7_28.2 [template = <error>]
+// CHECK:STDOUT:   assign %v.var, %.loc7_29
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT: