diff --git a/src/analyze.cpp b/src/analyze.cpp
index 1cb36682f9..263c04f6e4 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -161,18 +161,17 @@ static TypeTableEntry *new_container_type_entry(TypeTableEntryId id, AstNode *so
     return entry;
 }
 
+static uint8_t log2_u64(uint64_t x) {
+    return (63 - __builtin_clzll(x));
+}
 
-// TODO no reason to limit to 8/16/32/64
 static uint8_t bits_needed_for_unsigned(uint64_t x) {
-    if (x <= UINT8_MAX) {
-        return 8;
-    } else if (x <= UINT16_MAX) {
-        return 16;
-    } else if (x <= UINT32_MAX) {
-        return 32;
-    } else {
-        return 64;
+    if (x == 0) {
+        return 0;
     }
+    uint8_t base = log2_u64(x);
+    uint64_t upper = (((uint64_t)1) << base) - 1;
+    return (upper >= x) ? base : (base + 1);
 }
 
 bool type_is_complete(TypeTableEntry *type_entry) {
diff --git a/src/bigint.cpp b/src/bigint.cpp
index 5679d2041a..5c68b18a81 100644
--- a/src/bigint.cpp
+++ b/src/bigint.cpp
@@ -95,7 +95,9 @@ static void to_twos_complement(BigInt *dest, const BigInt *op, size_t bit_count)
 }
 
 static bool bit_at_index(const BigInt *bi, size_t index) {
-    size_t digit_index = bi->digit_count - (index / 64) - 1;
+    size_t digit_index = index / 64;
+    if (digit_index >= bi->digit_count)
+        return false;
     size_t digit_bit_index = index % 64;
     const uint64_t *digits = bigint_ptr(bi);
     uint64_t digit = digits[digit_index];
diff --git a/src/codegen.cpp b/src/codegen.cpp
index a7695d4d5f..7581ee271c 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -2440,25 +2440,27 @@ static LLVMValueRef get_int_builtin_fn(CodeGen *g, TypeTableEntry *int_type, Bui
 }
 
 static LLVMValueRef ir_render_clz(CodeGen *g, IrExecutable *executable, IrInstructionClz *instruction) {
-    TypeTableEntry *int_type = instruction->base.value.type;
+    TypeTableEntry *int_type = instruction->value->value.type;
     LLVMValueRef fn_val = get_int_builtin_fn(g, int_type, BuiltinFnIdClz);
     LLVMValueRef operand = ir_llvm_value(g, instruction->value);
     LLVMValueRef params[] {
         operand,
         LLVMConstNull(LLVMInt1Type()),
     };
-    return LLVMBuildCall(g->builder, fn_val, params, 2, "");
+    LLVMValueRef wrong_size_int = LLVMBuildCall(g->builder, fn_val, params, 2, "");
+    return gen_widen_or_shorten(g, false, int_type, instruction->base.value.type, wrong_size_int);
 }
 
 static LLVMValueRef ir_render_ctz(CodeGen *g, IrExecutable *executable, IrInstructionCtz *instruction) {
-    TypeTableEntry *int_type = instruction->base.value.type;
+    TypeTableEntry *int_type = instruction->value->value.type;
     LLVMValueRef fn_val = get_int_builtin_fn(g, int_type, BuiltinFnIdCtz);
     LLVMValueRef operand = ir_llvm_value(g, instruction->value);
     LLVMValueRef params[] {
         operand,
         LLVMConstNull(LLVMInt1Type()),
     };
-    return LLVMBuildCall(g->builder, fn_val, params, 2, "");
+    LLVMValueRef wrong_size_int = LLVMBuildCall(g->builder, fn_val, params, 2, "");
+    return gen_widen_or_shorten(g, false, int_type, instruction->base.value.type, wrong_size_int);
 }
 
 static LLVMValueRef ir_render_switch_br(CodeGen *g, IrExecutable *executable, IrInstructionSwitchBr *instruction) {
@@ -2545,7 +2547,8 @@ static LLVMValueRef ir_render_enum_tag_name(CodeGen *g, IrExecutable *executable
 
     LLVMValueRef indices[] = {
         LLVMConstNull(g->builtin_types.entry_usize->type_ref),
-        enum_tag_value,
+        gen_widen_or_shorten(g, false, enum_tag_type->data.enum_tag.int_type,
+                g->builtin_types.entry_usize, enum_tag_value),
     };
     return LLVMBuildInBoundsGEP(g->builder, enum_tag_type->data.enum_tag.name_table, indices, 2, "");
 }
diff --git a/src/ir.cpp b/src/ir.cpp
index 875be38654..57b7f07c20 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -11359,16 +11359,18 @@ static TypeTableEntry *ir_analyze_instruction_ctz(IrAnalyze *ira, IrInstructionC
     if (type_is_invalid(value->value.type)) {
         return ira->codegen->builtin_types.entry_invalid;
     } else if (value->value.type->id == TypeTableEntryIdInt) {
+        TypeTableEntry *return_type = get_smallest_unsigned_int_type(ira->codegen,
+                value->value.type->data.integral.bit_count);
         if (value->value.special != ConstValSpecialRuntime) {
             size_t result = bigint_ctz(&value->value.data.x_bigint,
                     value->value.type->data.integral.bit_count);
             ConstExprValue *out_val = ir_build_const_from(ira, &ctz_instruction->base);
             bigint_init_unsigned(&out_val->data.x_bigint, result);
-            return value->value.type;
+            return return_type;
         }
 
         ir_build_ctz_from(&ira->new_irb, &ctz_instruction->base, value);
-        return value->value.type;
+        return return_type;
     } else {
         ir_add_error_node(ira, ctz_instruction->base.source_node,
             buf_sprintf("expected integer type, found '%s'", buf_ptr(&value->value.type->name)));
@@ -11381,16 +11383,18 @@ static TypeTableEntry *ir_analyze_instruction_clz(IrAnalyze *ira, IrInstructionC
     if (type_is_invalid(value->value.type)) {
         return ira->codegen->builtin_types.entry_invalid;
     } else if (value->value.type->id == TypeTableEntryIdInt) {
+        TypeTableEntry *return_type = get_smallest_unsigned_int_type(ira->codegen,
+                value->value.type->data.integral.bit_count);
         if (value->value.special != ConstValSpecialRuntime) {
             size_t result = bigint_clz(&value->value.data.x_bigint,
                     value->value.type->data.integral.bit_count);
             ConstExprValue *out_val = ir_build_const_from(ira, &clz_instruction->base);
             bigint_init_unsigned(&out_val->data.x_bigint, result);
-            return value->value.type;
+            return return_type;
         }
 
         ir_build_clz_from(&ira->new_irb, &clz_instruction->base, value);
-        return value->value.type;
+        return return_type;
     } else {
         ir_add_error_node(ira, clz_instruction->base.source_node,
             buf_sprintf("expected integer type, found '%s'", buf_ptr(&value->value.type->name)));
diff --git a/std/special/compiler_rt/index.zig b/std/special/compiler_rt/index.zig
index c2486a3d59..0d2e1325ab 100644
--- a/std/special/compiler_rt/index.zig
+++ b/std/special/compiler_rt/index.zig
@@ -139,7 +139,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             // K X
             // ---
             // 0 K
-            sr = 1 + n_uword_bits + @clz(su_int(d[low])) - @clz(su_int(n[high]));
+            sr = 1 + n_uword_bits + c_uint(@clz(su_int(d[low]))) - c_uint(@clz(su_int(n[high])));
             // 2 <= sr <= n_udword_bits - 1
             // q.all = n.all << (n_udword_bits - sr);
             // r.all = n.all >> sr;
diff --git a/test/cases/math.zig b/test/cases/math.zig
index 82773f077a..5707e40607 100644
--- a/test/cases/math.zig
+++ b/test/cases/math.zig
@@ -66,6 +66,8 @@ fn testClz() {
     assert(clz(u8(0b00001010)) == 4);
     assert(clz(u8(0b10001010)) == 0);
     assert(clz(u8(0b00000000)) == 8);
+    assert(clz(u128(0xffffffffffffffff)) == 64);
+    assert(clz(u128(0x10000000000000000)) == 63);
 }
 
 fn clz(x: var) -> usize {