diff --git a/include/slang/syntax/SyntaxTree.h b/include/slang/syntax/SyntaxTree.h
index 04ae3e0da..93d667094 100644
--- a/include/slang/syntax/SyntaxTree.h
+++ b/include/slang/syntax/SyntaxTree.h
@@ -47,7 +47,7 @@ class SLANG_EXPORT SyntaxTree {
     bool isLibraryUnit = false;
 
     SyntaxTree(SyntaxNode* root, SourceManager& sourceManager, BumpAllocator&& alloc,
-               const SourceLibrary* library, std::shared_ptr<SyntaxTree> parent = nullptr);
+               const SourceLibrary* library, const std::shared_ptr<SyntaxTree>& parent = nullptr);
 
     SyntaxTree(SyntaxTree&& other) = default;
     ~SyntaxTree();
diff --git a/source/ast/statements/ConditionalStatements.cpp b/source/ast/statements/ConditionalStatements.cpp
index 1beb1e476..2b5d7e0c3 100644
--- a/source/ast/statements/ConditionalStatements.cpp
+++ b/source/ast/statements/ConditionalStatements.cpp
@@ -205,7 +205,7 @@ class CaseTrie {
         CaseTrie* curr = this;
         const auto width = value.getBitWidth();
         for (uint32_t i = 0; i < width; i++) {
-            const auto bit = value[i];
+            const auto bit = value[(int32_t)i];
             const bool isWildcard = wildcardX ? bit.isUnknown() : bit.value == logic_t::Z_VALUE;
             const auto valueIndex = isWildcard ? 3 : bit.isUnknown() ? 2 : bit.value;
 
@@ -226,7 +226,7 @@ class CaseTrie {
 private:
     const Expression* find(const SVInt& value, uint32_t bitIndex, const Expression& expr,
                            bool wildcardX) {
-        const auto bit = value[bitIndex];
+        const auto bit = value[(int32_t)bitIndex];
         const bool lastBit = bitIndex == value.getBitWidth() - 1;
         const bool isWildcard = wildcardX ? bit.isUnknown() : bit.value == logic_t::Z_VALUE;
         const auto valueIndex = bit.isUnknown() ? 2 : bit.value;
diff --git a/source/syntax/SyntaxTree.cpp b/source/syntax/SyntaxTree.cpp
index 06707b911..92f0c7819 100644
--- a/source/syntax/SyntaxTree.cpp
+++ b/source/syntax/SyntaxTree.cpp
@@ -18,7 +18,7 @@ namespace slang::syntax {
 using namespace parsing;
 
 SyntaxTree::SyntaxTree(SyntaxNode* root, SourceManager& sourceManager, BumpAllocator&& alloc,
-                       const SourceLibrary* library, std::shared_ptr<SyntaxTree> parent) :
+                       const SourceLibrary* library, const std::shared_ptr<SyntaxTree>& parent) :
     rootNode(root), library(library), sourceMan(sourceManager), alloc(std::move(alloc)) {
     metadata = std::make_unique<ParserMetadata>(ParserMetadata::fromSyntax(*root));
     if (parent) { // copy parent's info