diff --git a/mps/example/scheme/scheme-advanced.c b/mps/example/scheme/scheme-advanced.c
index accc65ab05f..2ce1e56d1c1 100644
--- a/mps/example/scheme/scheme-advanced.c
+++ b/mps/example/scheme/scheme-advanced.c
@@ -2979,7 +2979,7 @@ static obj_t entry_integer_to_char(obj_t env, obj_t op_env, obj_t operator, obj_
     error("%s: first argument must be an integer", operator->operator.name);
   unless(0 <= arg->integer.integer)
     error("%s: first argument is out of range", operator->operator.name);
-  return make_character(arg->integer.integer);
+  return make_character((char)arg->integer.integer);
 }
 
 
@@ -3059,7 +3059,7 @@ static obj_t entry_vector_ref(obj_t env, obj_t op_env, obj_t operator, obj_t ope
     error("%s: first argument must be a vector", operator->operator.name);
   unless(TYPE(index) == TYPE_INTEGER)
     error("%s: second argument must be an integer", operator->operator.name);
-  unless(0 <= index->integer.integer && index->integer.integer < vector->vector.length)
+  unless(0 <= index->integer.integer && (size_t)index->integer.integer < vector->vector.length)
     error("%s: index %ld out of bounds of vector length %ld",
           operator->operator.name, index->integer.integer, vector->vector.length);
   return vector->vector.vector[index->integer.integer];
@@ -3080,7 +3080,7 @@ static obj_t entry_vector_set(obj_t env, obj_t op_env, obj_t operator, obj_t ope
     error("%s: first argument must be a vector", operator->operator.name);
   unless(TYPE(index) == TYPE_INTEGER)
     error("%s: second argument must be an integer", operator->operator.name);
-  unless(0 <= index->integer.integer && index->integer.integer < vector->vector.length)
+  unless(0 <= index->integer.integer && (size_t)index->integer.integer < vector->vector.length)
     error("%s: index %ld out of bounds of vector length %ld",
           operator->operator.name, index->integer.integer, vector->vector.length);
   vector->vector.vector[index->integer.integer] = obj;
@@ -3293,7 +3293,7 @@ static obj_t entry_string_ref(obj_t env, obj_t op_env, obj_t operator, obj_t ope
     error("%s: first argument must be a string", operator->operator.name);
   unless(TYPE(k) == TYPE_INTEGER)
     error("%s: second argument must be an integer", operator->operator.name);
-  unless(0 <= k->integer.integer && k->integer.integer < arg->string.length)
+  unless(0 <= k->integer.integer && (size_t)k->integer.integer < arg->string.length)
     error("%s: second argument is out of range", operator->operator.name);
   return make_character(arg->string.string[k->integer.integer]);
 }
@@ -3337,7 +3337,7 @@ static obj_t entry_substring(obj_t env, obj_t op_env, obj_t operator, obj_t oper
     error("%s: third argument must be an integer", operator->operator.name);
   unless(0 <= start->integer.integer
          && start->integer.integer <= end->integer.integer
-         && end->integer.integer <= arg->string.length)
+         && (size_t)end->integer.integer <= arg->string.length)
     error("%s: arguments out of range", operator->operator.name);
   length = end->integer.integer - start->integer.integer;
   obj = make_string(length, NULL);