diff --git a/src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs b/src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
index 053c9035d8cce..1337c580d1f01 100644
--- a/src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
+++ b/src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
@@ -5614,8 +5614,8 @@ private TypeWithState ConvertConditionalOperandOrSwitchExpressionArmResult(
             LocalState state,
             bool isReachable)
         {
-            var savedState = this.State;
-            this.State = state;
+            var savedState = PossiblyConditionalState.Create(this);
+            this.SetState(state);
 
             bool previousDisabledDiagnostics = _disableDiagnostics;
             // If the node is not reachable, then we're only visiting to get
@@ -5644,7 +5644,7 @@ private TypeWithState ConvertConditionalOperandOrSwitchExpressionArmResult(
                 resultType = default;
                 _disableDiagnostics = previousDisabledDiagnostics;
             }
-            this.State = savedState;
+            this.SetPossiblyConditionalState(in savedState);
 
             return resultType;
         }
@@ -8457,8 +8457,7 @@ private TypeWithState VisitUserDefinedConversion(
             bool reportRemainingWarnings,
             Location diagnosticLocation)
         {
-            // Uncomment when https://github.com/dotnet/roslyn/issues/67153 is fixed
-            // Debug.Assert(!IsConditionalState);
+            Debug.Assert(!IsConditionalState);
             Debug.Assert(conversionOperand != null);
             Debug.Assert(targetTypeWithNullability.HasType);
             Debug.Assert(diagnosticLocation != null);
diff --git a/src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs b/src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs
index 73d4f82dc5b40..f72cf1ee35a60 100644
--- a/src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs
+++ b/src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs
@@ -53054,6 +53054,27 @@ static void M1(bool b, C c, D d)
             comp.VerifyDiagnostics();
         }
 
+        [Fact, WorkItem(67153, "https://github.com/dotnet/roslyn/issues/67153")]
+        public void ConditionalOperator_WithUserDefinedConversion_BoolOperand()
+        {
+            var source = """
+                struct C
+                {
+                    public static implicit operator C(bool b) => throw null!;
+                }
+                class D
+                {
+                    static void M(bool b)
+                    {
+                        _ = (b ? false : default(C)) /*T:C*/;
+                    }
+                }
+                """;
+            var comp = CreateCompilation(source, options: WithNullableEnable());
+            comp.VerifyTypes();
+            comp.VerifyDiagnostics();
+        }
+
         [Fact]
         [WorkItem(33664, "https://github.com/dotnet/roslyn/issues/33664")]
         public void ConditionalOperator_Ref_NestedNullabilityMismatch()