diff --git a/src/Bicep.Core.IntegrationTests/ParametersTests.cs b/src/Bicep.Core.IntegrationTests/ParametersTests.cs
index 5689be3fb9a..1f1ce6f97d3 100644
--- a/src/Bicep.Core.IntegrationTests/ParametersTests.cs
+++ b/src/Bicep.Core.IntegrationTests/ParametersTests.cs
@@ -673,6 +673,185 @@ param values array
             }"));
         }
 
+        [TestMethod]
+        public void Base_object_spread_should_not_evaluate_unreferenced_external_input()
+        {
+            var result = CompilationHelper.CompileParams(
+              ("parameters.bicepparam", @"
+                using 'main.bicep'
+                extends 'shared.bicepparam'
+                param B = {
+                  ...base.B
+                  something: 'something'
+                }
+              "),
+              ("shared.bicepparam", @"
+                using none
+                param external = externalInput('foo', 'bar')
+                param B = {
+                  parent: 'parent'
+                }
+              "),
+              ("main.bicep", @"
+                param external object
+                param B object
+              "));
+
+            result.ExcludingLinterDiagnostics().Should().NotHaveAnyDiagnostics();
+            result.Parameters.Should().HaveJsonAtPath("parameters.B.value", @"{
+              ""parent"": ""parent"",
+              ""something"": ""something""
+            }");
+            result.Parameters.Should().HaveValueAtPath("parameters.external.expression", "[externalInputs('foo_0')]");
+            result.Parameters.Should().HaveJsonAtPath("externalInputDefinitions", @"{
+              ""foo_0"": {
+                ""kind"": ""foo"",
+                ""config"": ""bar""
+              }
+            }");
+        }
+
+        [TestMethod]
+        public void Base_array_spread_should_not_evaluate_unreferenced_external_input()
+        {
+            var result = CompilationHelper.CompileParams(
+              ("parameters.bicepparam", @"
+                using 'main.bicep'
+                extends 'shared.bicepparam'
+                param values = [
+                  ...base.values
+                  'child'
+                ]
+              "),
+              ("shared.bicepparam", @"
+                using none
+                param enabled = bool(externalInput('feature', 'enabled'))
+                param values = [
+                  'parent'
+                ]
+              "),
+              ("main.bicep", @"
+                param enabled bool
+                param values array
+              "));
+
+            result.ExcludingLinterDiagnostics().Should().NotHaveAnyDiagnostics();
+            result.Parameters.Should().HaveJsonAtPath("parameters.values.value", @"[
+              ""parent"",
+              ""child""
+            ]");
+            result.Parameters.Should().HaveValueAtPath("parameters.enabled.expression", "[bool(externalInputs('feature_0'))]");
+            result.Parameters.Should().HaveJsonAtPath("externalInputDefinitions", @"{
+              ""feature_0"": {
+                ""kind"": ""feature"",
+                ""config"": ""enabled""
+              }
+            }");
+        }
+
+        [TestMethod]
+        public void Base_property_accesses_should_not_evaluate_unreferenced_external_input()
+        {
+            var result = CompilationHelper.CompileParams(
+              ("parameters.bicepparam", @"
+                using 'main.bicep'
+                extends 'shared.bicepparam'
+                param dotAccess = base.selected.value
+                param bracketAccess = base['selected'].value
+              "),
+              ("shared.bicepparam", @"
+                using none
+                param external = externalInput('foo')
+                param selected = {
+                  value: 'parent'
+                }
+              "),
+              ("main.bicep", @"
+                param external object
+                param selected object
+                param dotAccess string
+                param bracketAccess string
+              "));
+
+            result.ExcludingLinterDiagnostics().Should().NotHaveAnyDiagnostics();
+            result.Parameters.Should().HaveValueAtPath("parameters.dotAccess.value", "parent");
+            result.Parameters.Should().HaveValueAtPath("parameters.bracketAccess.value", "parent");
+            result.Parameters.Should().HaveValueAtPath("parameters.external.expression", "[externalInputs('foo_0')]");
+        }
+
+        [TestMethod]
+        public void Nested_base_spreads_should_not_evaluate_unreferenced_external_input()
+        {
+            var result = CompilationHelper.CompileParams(
+              ("parameters.bicepparam", @"
+                using 'main.bicep'
+                extends 'middle.bicepparam'
+                param tags = {
+                  ...base.tags
+                  child: 'child'
+                }
+              "),
+              ("middle.bicepparam", @"
+                using none
+                extends 'base.bicepparam'
+                param tags = {
+                  ...base.tags
+                  middle: 'middle'
+                }
+              "),
+              ("base.bicepparam", @"
+                using none
+                param external = externalInput('foo')
+                param tags = {
+                  parent: 'parent'
+                }
+              "),
+              ("main.bicep", @"
+                param external object
+                param tags object
+              "));
+
+            result.ExcludingLinterDiagnostics().Should().NotHaveAnyDiagnostics();
+            result.Parameters.Should().HaveJsonAtPath("parameters.tags.value", @"{
+              ""parent"": ""parent"",
+              ""middle"": ""middle"",
+              ""child"": ""child""
+            }");
+            result.Parameters.Should().HaveValueAtPath("parameters.external.expression", "[externalInputs('foo_0')]");
+        }
+
+        [TestMethod]
+        public void Base_spread_should_preserve_function_bindings_in_selected_parent_parameter()
+        {
+            var result = CompilationHelper.CompileParams(
+              ("parameters.bicepparam", @"
+                using 'main.bicep'
+                extends 'shared.bicepparam'
+                param tags = {
+                  ...base.tags
+                  child: 'child'
+                }
+              "),
+              ("shared.bicepparam", @"
+                using none
+                param external = externalInput('foo')
+                param tags = {
+                  parent: toLower('PARENT')
+                }
+              "),
+              ("main.bicep", @"
+                param external object
+                param tags object
+              "));
+
+            result.ExcludingLinterDiagnostics().Should().NotHaveAnyDiagnostics();
+            result.Parameters.Should().HaveJsonAtPath("parameters.tags.value", @"{
+              ""parent"": ""parent"",
+              ""child"": ""child""
+            }");
+            result.Parameters.Should().HaveValueAtPath("parameters.external.expression", "[externalInputs('foo_0')]");
+        }
+
         [TestMethod]
         public void Decorators_on_using_param_and_extends_statements_should_raise_errors()
         {
diff --git a/src/Bicep.Core/Intermediate/ExpressionBuilder.cs b/src/Bicep.Core/Intermediate/ExpressionBuilder.cs
index d8851710da3..82ac1b91121 100644
--- a/src/Bicep.Core/Intermediate/ExpressionBuilder.cs
+++ b/src/Bicep.Core/Intermediate/ExpressionBuilder.cs
@@ -979,6 +979,13 @@ private Expression ConvertArrayAccess(ArrayAccessSyntax arrayAccess)
             }
         }
 
+        if (arrayAccess.IndexExpression is StringSyntax indexString &&
+            indexString.TryGetLiteralValue() is { } propertyName &&
+            TryGetBaseParameterAssignment(arrayAccess.BaseExpression, propertyName) is { } parentAssignment)
+        {
+            return ConvertWithoutLowering(parentAssignment.DeclaringParameterAssignment.Value);
+        }
+
         var convertedBase = ConvertWithoutLowering(arrayAccess.BaseExpression);
         var convertedIndex = ConvertWithoutLowering(arrayAccess.IndexExpression);
 
@@ -1030,6 +1037,11 @@ private Expression ConvertPropertyAccess(PropertyAccessSyntax propertyAccess)
     {
         var flags = GetAccessExpressionFlags(propertyAccess);
 
+        if (TryGetBaseParameterAssignment(propertyAccess.BaseExpression, propertyAccess.PropertyName.IdentifierName) is { } parentAssignment)
+        {
+            return ConvertWithoutLowering(parentAssignment.DeclaringParameterAssignment.Value);
+        }
+
         // Looking for: myResource.someProp (where myResource is a resource declared in-file)
         if (Context.SemanticModel.ResourceMetadata.TryLookup(propertyAccess.BaseExpression) is DeclaredResourceMetadata resource)
         {
@@ -1098,6 +1110,11 @@ moduleCollectionOutputs.BaseExpression is ArrayAccessSyntax moduleArrayAccess &&
             flags);
     }
 
+    private ParameterAssignmentSymbol? TryGetBaseParameterAssignment(SyntaxBase baseExpression, string propertyName)
+        => Context.SemanticModel.GetSymbolInfo(baseExpression) is BaseParametersSymbol baseParameters
+            ? baseParameters.ParentAssignments.FirstOrDefault(assignment => LanguageConstants.IdentifierComparer.Equals(assignment.Name, propertyName))
+            : null;
+
     private Expression ConvertResourceAccess(ResourceAccessSyntax resourceAccessSyntax)
     {
         if (Context.SemanticModel.ResourceMetadata.TryLookup(resourceAccessSyntax) is { } resource)