diff --git a/toolchain/semantics/semantics_context.cpp b/toolchain/semantics/semantics_context.cpp
index e0b813e0da53..1ca8a3657eef 100644
--- a/toolchain/semantics/semantics_context.cpp
+++ b/toolchain/semantics/semantics_context.cpp
@@ -68,10 +68,7 @@ auto SemanticsContext::AddNodeAndPush(ParseTree::Node parse_node,
 auto SemanticsContext::AddNameToLookup(ParseTree::Node name_node,
                                        SemanticsStringId name_id,
                                        SemanticsNodeId target_id) -> void {
-  auto [it, inserted] = current_scope().names.insert(name_id);
-  if (inserted) {
-    name_lookup_[name_id].push_back(target_id);
-  } else {
+  if (!AddNameToLookupImpl(name_id, target_id)) {
     CARBON_DIAGNOSTIC(NameRedefined, Error, "Redefining {0} in the same scope.",
                       llvm::StringRef);
     CARBON_DIAGNOSTIC(PreviousDefinition, Note, "Previous definition is here.");
@@ -84,6 +81,16 @@ auto SemanticsContext::AddNameToLookup(ParseTree::Node name_node,
   }
 }
 
+auto SemanticsContext::AddNameToLookupImpl(SemanticsStringId name_id,
+                                           SemanticsNodeId target_id) -> bool {
+  if (current_scope().names.insert(name_id).second) {
+    name_lookup_[name_id].push_back(target_id);
+    return true;
+  } else {
+    return false;
+  }
+}
+
 auto SemanticsContext::BindName(ParseTree::Node name_node,
                                 SemanticsNodeId type_id,
                                 SemanticsNodeId target_id)
diff --git a/toolchain/semantics/semantics_context.h b/toolchain/semantics/semantics_context.h
index 29d122264595..b5d4db56247c 100644
--- a/toolchain/semantics/semantics_context.h
+++ b/toolchain/semantics/semantics_context.h
@@ -38,10 +38,17 @@ class SemanticsContext {
   // result.
   auto AddNodeAndPush(ParseTree::Node parse_node, SemanticsNode node) -> void;
 
-  // Adds a name to name lookup.
+  // Adds a name to name lookup. Prints a diagnostic for name conflicts.
   auto AddNameToLookup(ParseTree::Node name_node, SemanticsStringId name_id,
                        SemanticsNodeId target_id) -> void;
 
+  // Adds a name to name lookup. Ignores any name conflicts; the caller should
+  // ensure they were previously diagnosed by AddNameToLookup.
+  auto AddNameToLookupIgnoreConflicts(SemanticsStringId name_id,
+                                      SemanticsNodeId target_id) -> void {
+    AddNameToLookupImpl(name_id, target_id);
+  }
+
   // Binds a DeclaredName to a target node with the given type.
   auto BindName(ParseTree::Node name_node, SemanticsNodeId type_id,
                 SemanticsNodeId target_id) -> SemanticsStringId;
@@ -170,6 +177,10 @@ class SemanticsContext {
     // TODO: This likely needs to track things which need to be destructed.
   };
 
+  // Adds a name to lookup. Returns false on a name conflict.
+  auto AddNameToLookupImpl(SemanticsStringId name_id, SemanticsNodeId target_id)
+      -> bool;
+
   // Runs ImplicitAs behavior to convert `value` to `as_type`, returning the
   // result type. The result will be the node to use to replace `value`.
   //
diff --git a/toolchain/semantics/semantics_handle_function.cpp b/toolchain/semantics/semantics_handle_function.cpp
index 43a5fcee61be..22141940dbf3 100644
--- a/toolchain/semantics/semantics_handle_function.cpp
+++ b/toolchain/semantics/semantics_handle_function.cpp
@@ -58,6 +58,11 @@ auto SemanticsHandleFunctionDefinitionStart(SemanticsContext& context,
 
   context.node_block_stack().Push();
   context.PushScope();
+  for (auto ref_id : context.semantics().GetNodeBlock(param_refs_id)) {
+    auto ref = context.semantics().GetNode(ref_id);
+    auto [name_id, target_id] = ref.GetAsBindName();
+    context.AddNameToLookupIgnoreConflicts(name_id, target_id);
+  }
   context.return_scope_stack().push_back(decl_id);
   context.node_stack().Push(parse_node, decl_id);
 
diff --git a/toolchain/semantics/testdata/function/call/empty_struct.carbon b/toolchain/semantics/testdata/function/call/empty_struct.carbon
index 7524e7ee53e2..eb628dfa3b0e 100644
--- a/toolchain/semantics/testdata/function/call/empty_struct.carbon
+++ b/toolchain/semantics/testdata/function/call/empty_struct.carbon
@@ -5,7 +5,7 @@
 // AUTOUPDATE
 // CHECK:STDOUT: cross_reference_irs_size: 1
 // CHECK:STDOUT: callables: [
-// CHECK:STDOUT:   {param_refs: block2},
+// CHECK:STDOUT:   {param_refs: block2, return_type: nodeEmptyStructType},
 // CHECK:STDOUT:   {param_refs: block0},
 // CHECK:STDOUT: ]
 // CHECK:STDOUT: integer_literals: [
@@ -21,11 +21,12 @@
 // CHECK:STDOUT:   {kind: VarStorage, type: nodeEmptyStructType},
 // CHECK:STDOUT:   {kind: BindName, arg0: str0, arg1: node+0, type: nodeEmptyStructType},
 // CHECK:STDOUT:   {kind: FunctionDeclaration, arg0: str1, arg1: callable0},
-// CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+2, arg1: block0},
+// CHECK:STDOUT:   {kind: ReturnExpression, arg0: node+0, type: nodeEmptyStructType},
+// CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+2, arg1: block4},
 // CHECK:STDOUT:   {kind: FunctionDeclaration, arg0: str2, arg1: callable1},
 // CHECK:STDOUT:   {kind: StubReference, arg0: nodeEmptyStruct, type: nodeEmptyStructType},
-// CHECK:STDOUT:   {kind: Call, arg0: block5, arg1: callable0},
-// CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+4, arg1: block4},
+// CHECK:STDOUT:   {kind: Call, arg0: block6, arg1: callable0, type: nodeEmptyStructType},
+// CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+5, arg1: block5},
 // CHECK:STDOUT: ]
 // CHECK:STDOUT: node_blocks: [
 // CHECK:STDOUT:   [
@@ -39,20 +40,24 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT:   [
 // CHECK:STDOUT:     node+2,
-// CHECK:STDOUT:     node+3,
 // CHECK:STDOUT:     node+4,
+// CHECK:STDOUT:     node+5,
+// CHECK:STDOUT:     node+8,
+// CHECK:STDOUT:   ],
+// CHECK:STDOUT:   [
+// CHECK:STDOUT:     node+3,
+// CHECK:STDOUT:   ],
+// CHECK:STDOUT:   [
+// CHECK:STDOUT:     node+6,
 // CHECK:STDOUT:     node+7,
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT:   [
-// CHECK:STDOUT:     node+5,
 // CHECK:STDOUT:     node+6,
 // CHECK:STDOUT:   ],
-// CHECK:STDOUT:   [
-// CHECK:STDOUT:     node+5,
-// CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-fn Echo(a: {}) {
+fn Echo(a: {}) -> {} {
+  return a;
 }
 
 fn Main() {
diff --git a/toolchain/semantics/testdata/function/call/i32.carbon b/toolchain/semantics/testdata/function/call/i32.carbon
index adf206e13b3a..e20487e3277e 100644
--- a/toolchain/semantics/testdata/function/call/i32.carbon
+++ b/toolchain/semantics/testdata/function/call/i32.carbon
@@ -10,7 +10,6 @@
 // CHECK:STDOUT: ]
 // CHECK:STDOUT: integer_literals: [
 // CHECK:STDOUT:   1,
-// CHECK:STDOUT:   1,
 // CHECK:STDOUT: ]
 // CHECK:STDOUT: real_literals: [
 // CHECK:STDOUT: ]
@@ -24,17 +23,16 @@
 // CHECK:STDOUT:   {kind: VarStorage, type: nodeIntegerType},
 // CHECK:STDOUT:   {kind: BindName, arg0: str0, arg1: node+0, type: nodeIntegerType},
 // CHECK:STDOUT:   {kind: FunctionDeclaration, arg0: str1, arg1: callable0},
-// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int0, type: nodeIntegerType},
-// CHECK:STDOUT:   {kind: ReturnExpression, arg0: node+3, type: nodeIntegerType},
+// CHECK:STDOUT:   {kind: ReturnExpression, arg0: node+0, type: nodeIntegerType},
 // CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+2, arg1: block4},
 // CHECK:STDOUT:   {kind: FunctionDeclaration, arg0: str2, arg1: callable1},
 // CHECK:STDOUT:   {kind: VarStorage, type: nodeIntegerType},
-// CHECK:STDOUT:   {kind: BindName, arg0: str3, arg1: node+7, type: nodeIntegerType},
-// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int1, type: nodeIntegerType},
-// CHECK:STDOUT:   {kind: StubReference, arg0: node+9, type: nodeIntegerType},
+// CHECK:STDOUT:   {kind: BindName, arg0: str3, arg1: node+6, type: nodeIntegerType},
+// CHECK:STDOUT:   {kind: IntegerLiteral, arg0: int0, type: nodeIntegerType},
+// CHECK:STDOUT:   {kind: StubReference, arg0: node+8, type: nodeIntegerType},
 // CHECK:STDOUT:   {kind: Call, arg0: block6, arg1: callable0, type: nodeIntegerType},
-// CHECK:STDOUT:   {kind: Assign, arg0: node+7, arg1: node+11, type: nodeIntegerType},
-// CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+6, arg1: block5},
+// CHECK:STDOUT:   {kind: Assign, arg0: node+6, arg1: node+10, type: nodeIntegerType},
+// CHECK:STDOUT:   {kind: FunctionDefinition, arg0: node+5, arg1: block5},
 // CHECK:STDOUT: ]
 // CHECK:STDOUT: node_blocks: [
 // CHECK:STDOUT:   [
@@ -48,30 +46,28 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT:   [
 // CHECK:STDOUT:     node+2,
+// CHECK:STDOUT:     node+4,
 // CHECK:STDOUT:     node+5,
-// CHECK:STDOUT:     node+6,
-// CHECK:STDOUT:     node+13,
+// CHECK:STDOUT:     node+12,
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT:   [
 // CHECK:STDOUT:     node+3,
-// CHECK:STDOUT:     node+4,
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT:   [
+// CHECK:STDOUT:     node+6,
 // CHECK:STDOUT:     node+7,
 // CHECK:STDOUT:     node+8,
 // CHECK:STDOUT:     node+9,
 // CHECK:STDOUT:     node+10,
 // CHECK:STDOUT:     node+11,
-// CHECK:STDOUT:     node+12,
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT:   [
-// CHECK:STDOUT:     node+10,
+// CHECK:STDOUT:     node+9,
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
 fn Echo(a: i32) -> i32 {
-  // TODO: `return a;` requires the parameter to be in name lookup.
-  return 1;
+  return a;
 }
 
 fn Main() {