diff --git a/self_hosted/typecheck.jou b/self_hosted/typecheck.jou
index 27e64fce..2b9d18f5 100644
--- a/self_hosted/typecheck.jou
+++ b/self_hosted/typecheck.jou
@@ -1026,11 +1026,17 @@ class Stage3TypeChecker:
             snprintf(message, sizeof message[0], "value of type %s cannot be indexed", types->original_type->name)
             fail(pointer->location, message)
 
-        index_type = self->do_expression(index)->original_type
-        if not index_type->is_integer_type():
-            snprintf(message, sizeof message[0], "the index inside [...] must be an integer, not %s", index_type->name)
+        index_types = self->do_expression(index)
+        assert index_types != NULL
+
+        if not index_types->original_type->is_integer_type():
+            snprintf(message, sizeof message[0], "the index inside [...] must be an integer, not %s", index_types->original_type->name)
             fail(index->location, message)
 
+        # LLVM assumes that indexes smaller than 64 bits are signed.
+        # https://github.com/Akuli/jou/issues/48
+        index_types->do_implicit_cast(long_type, Location{}, NULL)
+
         return pointer_type->value_type
 
     def do_expression_maybe_void(self, expression: AstExpression*) -> ExpressionTypes*:
diff --git a/src/codegen.c b/src/codegen.c
index 2a36a52f..313b5de4 100644
--- a/src/codegen.c
+++ b/src/codegen.c
@@ -336,15 +336,7 @@ static void codegen_instruction(const struct State *st, const CfInstruction *ins
             }
             break;
         case CF_PTR_ADD_INT:
-            {
-                LLVMValueRef index = getop(1);
-                if (ins->operands[1]->type->kind == TYPE_UNSIGNED_INTEGER) {
-                    // https://github.com/Akuli/jou/issues/48
-                    // Apparently the default is to interpret indexes as signed.
-                    index = LLVMBuildZExt(st->builder, index, LLVMInt64Type(), "ptr_add_int_implicit_cast");
-                }
-                setdest(LLVMBuildGEP(st->builder, getop(0), &index, 1, "ptr_add_int"));
-            }
+            setdest(LLVMBuildGEP(st->builder, getop(0), (LLVMValueRef[]){getop(1)}, 1, "ptr_add_int"));
             break;
         case CF_NUM_CAST:
             {
diff --git a/src/typecheck.c b/src/typecheck.c
index 029d7fe4..2f3069c7 100644
--- a/src/typecheck.c
+++ b/src/typecheck.c
@@ -756,14 +756,18 @@ static const Type *typecheck_indexing(
     }
     assert(ptrtype->kind == TYPE_POINTER);
 
-    const Type *indextype = typecheck_expression_not_void(ft, indexexpr)->type;
-    if (!is_integer_type(indextype)) {
+    ExpressionTypes *indextypes = typecheck_expression_not_void(ft, indexexpr);
+    if (!is_integer_type(indextypes->type)) {
         fail_with_error(
             indexexpr->location,
             "the index inside [...] must be an integer, not %s",
-            indextype->name);
+            indextypes->type->name);
     }
 
+    // LLVM assumes that indexes smaller than 64 bits are signed.
+    // https://github.com/Akuli/jou/issues/48
+    do_implicit_cast(indextypes, longType, (Location){0}, NULL);
+
     return ptrtype->data.valuetype;
 }