diff --git a/src/builtins.c b/src/builtins.c
index 17cf078..27159d7 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -12,15 +12,15 @@
 LISP_FUNC_1(ucl_builtin_type, state, arg) {
     switch (arg->type) {
         case UCL_TYPE_CELL:
-            return ucl_symbol_create(strdup("list"));
+            return ucl_symbol_create("list");
         case UCL_TYPE_SYMBOL:
-            return ucl_symbol_create(strdup("symbol"));
+            return ucl_symbol_create("symbol");
         case UCL_TYPE_INT:
-            return ucl_symbol_create(strdup("int"));
+            return ucl_symbol_create("int");
         case UCL_TYPE_STRING:
-            return ucl_symbol_create(strdup("string"));
+            return ucl_symbol_create("string");
         case UCL_TYPE_ERROR:
-            return ucl_symbol_create(strdup("error"));
+            return ucl_symbol_create("error");
         case UCL_TYPE_COUNT:
             assert(0);
             return NULL;
@@ -32,7 +32,7 @@ LISP_FUNC_1(ucl_builtin_error, state, arg) {
         return ucl_error_create("Expected type string passed to 'error'");
     }
 
-    return ucl_error_create(strdup(arg->error));
+    return ucl_error_create(arg->error);
 }
 
 LISP_FUNC_1(ucl_builtin_symbol_p, state, arg) {
@@ -81,7 +81,7 @@ LISP_FUNC_2(ucl_builtin_sub, state, arg0, arg1) {
     }
 
     if (arg1->type != UCL_TYPE_INT) {
-        return ucl_error_create("Invalid type of argument 1 to 'sub'");
+        return ucl_error_create(("Invalid type of argument 1 to 'sub'"));
     }
 
     return ucl_int_create(arg0->integer - arg1->integer);
diff --git a/src/evaluate.c b/src/evaluate.c
index da0dbb7..03d1fb6 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -6,6 +6,7 @@
 #include "utility.h"
 #include "state.h"
 
+// TODO: remove string.h
 #include <string.h>
 
 struct ucl_object *ucl_evaluate_list(struct ucl_state *state, struct ucl_object *list) {
diff --git a/src/memory.c b/src/memory.c
index 82e9527..631d490 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -3,7 +3,7 @@
 
 #include <stddef.h>
 #include <stdlib.h>
-
+#include <string.h>
 
 static struct ucl_object *ucl_object_alloc();
 
@@ -28,7 +28,7 @@ struct ucl_object *ucl_symbol_create(const char *symbol)
 {
     struct ucl_object* obj = ucl_object_alloc();
     obj->type = UCL_TYPE_SYMBOL;
-    obj->symbol = symbol;
+    obj->symbol = strdup(symbol);
     return obj;
 }
 
@@ -36,7 +36,7 @@ struct ucl_object *ucl_string_create(const char *string)
 {
     struct ucl_object* obj = ucl_object_alloc();
     obj->type = UCL_TYPE_STRING;
-    obj->string = string;
+    obj->string = strdup(string);
     return obj;
 }
 
@@ -44,7 +44,7 @@ struct ucl_object *ucl_error_create(const char *error)
 {
     struct ucl_object* obj = ucl_object_alloc();
     obj->type = UCL_TYPE_ERROR;
-    obj->error = error;
+    obj->error = strdup(error);
     return obj;
 }
 
diff --git a/src/parse.c b/src/parse.c
index 091cdca..4113666 100644
--- a/src/parse.c
+++ b/src/parse.c
@@ -113,11 +113,11 @@ struct ucl_object *ucl_parse_token_atom(struct ucl_object *maybe_atom) {
                     return NULL;
                 }
             }
-            atom = ucl_symbol_create(strdup(maybe_atom->symbol));
+            atom = ucl_symbol_create(maybe_atom->symbol);
             break;
         }
         case UCL_TYPE_STRING:
-            atom = ucl_string_create(strdup(maybe_atom->string));
+            atom = ucl_string_create(maybe_atom->string);
             break;
         case UCL_TYPE_INT:
             atom = ucl_int_create(maybe_atom->integer);
diff --git a/src/state.c b/src/state.c
index 021ea1c..1daf50b 100644
--- a/src/state.c
+++ b/src/state.c
@@ -34,7 +34,7 @@ struct ucl_object *ucl_state_get(struct ucl_state *state, const char *name) {
     struct ucl_object *cell = ucl_state_get_cell(state, name);
     if (cell == NULL) {
         if (state->parent == NULL) {
-            return ucl_error_create(strdup("Unknown error"));
+            return ucl_error_create("Unknown error");
         } else {
             return ucl_state_get(state->parent, name);
         }
@@ -47,7 +47,7 @@ void ucl_state_put(struct ucl_state *state, const char *name, struct ucl_object
     if (cell == NULL) {
         ucl_list_append(state->list,
                        ucl_tuple_create(
-                           ucl_string_create(strdup(name)),
+                           ucl_string_create(name),
                            obj));
     } else {
         // TODO: Refcounting / cleanup
diff --git a/src/utility.c b/src/utility.c
index b5a242a..5e4f171 100644
--- a/src/utility.c
+++ b/src/utility.c
@@ -37,7 +37,7 @@ struct ucl_object *ucl_nil_create() {
 }
 
 struct ucl_object *ucl_t_create() {
-    return ucl_symbol_create(strdup("t"));
+    return ucl_symbol_create("t");
 }
 
 struct ucl_object *ucl_predicate(bool value) {
diff --git a/src/utility.h b/src/utility.h
index 4151760..030535e 100644
--- a/src/utility.h
+++ b/src/utility.h
@@ -25,11 +25,11 @@ struct ucl_object* ucl_tuple_create(struct ucl_object *obj0, struct ucl_object *
         return obj;                             \
     } while(0)
 
-#define UCL_COND_OR_RET_ERROR(cond, msg)            \
-    do {                                            \
-        if (!(cond)) {                              \
-            return ucl_error_create(strdup(msg));   \
-        }                                           \
+#define UCL_COND_OR_RET_ERROR(cond, msg)        \
+    do {                                        \
+        if (!(cond)) {                          \
+            return ucl_error_create(msg);       \
+        }                                       \
     } while(0)
 
 #endif
diff --git a/test/test_e2e.c b/test/test_e2e.c
index 69b6444..e4c858f 100644
--- a/test/test_e2e.c
+++ b/test/test_e2e.c
@@ -103,6 +103,12 @@ static void test_eval_sym_undefined(void) {
     TEST_ASSERT_OBJ_ERROR(response);
 }
 
+static void test_eval_nested_error(void) {
+    response = eval("(+ (error \"foo\") 3)");
+    TEST_ASSERT_OBJ_ERROR(response);
+}
+
+
 int main(void) {
     UNITY_BEGIN();
 
@@ -117,6 +123,7 @@ int main(void) {
     RUN_TEST(test_eval_string);
     RUN_TEST(test_eval_sym_defined);
     RUN_TEST(test_eval_sym_undefined);
+    RUN_TEST(test_eval_nested_error);
 
     return UNITY_END();
 }
diff --git a/test/test_parse.c b/test/test_parse.c
index e124054..18ccba0 100644
--- a/test/test_parse.c
+++ b/test/test_parse.c
@@ -188,20 +188,20 @@ static void test_tokenize_statement(void) {
 }
 
 static void test_parse_atom_symbol(void) {
-    response = ucl_parse_token_atom(ucl_symbol_create(strdup("foo")));
+    response = ucl_parse_token_atom(ucl_symbol_create("foo"));
 
     TEST_ASSERT_EQUAL(response->type, UCL_TYPE_SYMBOL);
     TEST_ASSERT_EQUAL_STRING(response->symbol, "foo");
 }
 
 static void test_parse_atom_lparen(void) {
-    response = ucl_parse_token_atom(ucl_symbol_create(strdup("(")));
+    response = ucl_parse_token_atom(ucl_symbol_create("("));
 
     TEST_ASSERT_NULL(response);
 }
 
 static void test_parse_atom_rparen(void) {
-    response = ucl_parse_token_atom(ucl_symbol_create(strdup(")")));
+    response = ucl_parse_token_atom(ucl_symbol_create(")"));
 
     TEST_ASSERT_NULL(response);
 }
diff --git a/test/test_state.c b/test/test_state.c
index 11f6703..576ee4a 100644
--- a/test/test_state.c
+++ b/test/test_state.c
@@ -41,11 +41,11 @@ static void test_put2_get(void) {
 
 static void test_put_modify_get(void) {
     struct ucl_object *obj = ucl_tuple_create(
-        ucl_string_create(strdup("bar")),
-        ucl_string_create(strdup("baz")));
+        ucl_string_create("bar"),
+        ucl_string_create("baz"));
 
     ucl_state_put(state, "foo", obj);
-    ucl_list_append(obj, ucl_string_create(strdup("quux")));
+    ucl_list_append(obj, ucl_string_create("quux"));
     response = ucl_state_get(state, "foo");
 
     TEST_ASSERT_OBJ_STRING(ucl_list_nth(response, 2));
diff --git a/test/test_utility.c b/test/test_utility.c
index 78f0a5c..7dd49f1 100644
--- a/test/test_utility.c
+++ b/test/test_utility.c
@@ -73,7 +73,7 @@ static void test_cdr_t(void) {
 
 static void test_car_list(void) {
     input = ucl_tuple_create(
-        ucl_string_create(strdup("foo")),
+        ucl_string_create("foo"),
         ucl_t_create());
     response = ucl_car(input);
 
@@ -83,7 +83,7 @@ static void test_car_list(void) {
 static void test_cdr_list(void) {
     input = ucl_tuple_create(
         ucl_t_create(),
-        ucl_string_create(strdup("foo")));
+        ucl_string_create("foo"));
     response = ucl_cdr(input);
 
     TEST_ASSERT_OBJ_STRING(ucl_car(response));
@@ -146,7 +146,7 @@ static void test_list_nth_list_0() {
     response = ucl_list_nth(
         ucl_tuple_create(
             ucl_t_create(),
-            ucl_string_create(strdup("foo"))),
+            ucl_string_create("foo")),
         0);
 
     TEST_ASSERT_T(response);
@@ -156,7 +156,7 @@ static void test_list_nth_list_1() {
     response = ucl_list_nth(
         ucl_tuple_create(
             ucl_t_create(),
-            ucl_string_create(strdup("foo"))),
+            ucl_string_create("foo")),
         1);
 
     TEST_ASSERT_OBJ_STRING(response);