diff --git a/Makefile b/Makefile
index 9d8d127..35cfd26 100644
--- a/Makefile
+++ b/Makefile
@@ -32,13 +32,13 @@ build/test/%.o: test/%.c ${HEADER_FILES} | build/test
 .PHONY: run
 run: ${LIB} ./main.c
 	mkdir --parents ./bin
-	${CC} ${CC_FLAGS} -o ${MAIN_EXECUTABLE} ./main.c ${LIB_CC_FLAGS}
+	${CC} ${CC_FLAGS} ${CC_SANITIZER_FLAGS} -o ${MAIN_EXECUTABLE} ./main.c ${LIB_CC_FLAGS}
 	./${MAIN_EXECUTABLE} ${ARGS}
 
 .PHONY: set_version
 set_version: ${LIB} ./set_version.c
 	mkdir --parents ./bin
-	${CC} ${CC_FLAGS} -o ${SET_VERSION_EXECUTABLE} ./set_version.c ${LIB_CC_FLAGS}
+	${CC} ${CC_FLAGS} ${CC_SANITIZER_FLAGS} -o ${SET_VERSION_EXECUTABLE} ./set_version.c ${LIB_CC_FLAGS}
 
 .PHONY: test
 test: ${LIB} $(addprefix build/, ${TEST_OBJECTS})
diff --git a/lib/string.c b/lib/string.c
index 4d3fdbb..258176d 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -212,24 +212,20 @@ string_t string_join(string_t* array, const char separator, size_t array_length)
   return string;
 }
 
-string_t string_concatenate(string_t string1, string_t string2) {
-  size_t string1_length = string_get_length(string1);
-  size_t string2_length = string_get_length(string2);
-  size_t result_length = string1_length + string2_length;
-  string_t result = malloc(sizeof(char) * (result_length + 1));
-  if (result == NULL) {
+void string_concatenate(string_t* destination, string_t source) {
+  size_t destination_length = string_get_length(*destination);
+  size_t source_length = string_get_length(source);
+  size_t new_length = destination_length + source_length;
+  *destination = realloc(*destination, sizeof(char) * (new_length + 1));
+  if (*destination == NULL) {
     perror("Error (string_concatenate)");
     exit(EXIT_FAILURE);
   }
-  size_t index_string1 = 0;
-  for (; index_string1 < string1_length; index_string1++) {
-    result[index_string1] = string1[index_string1];
+  size_t index_destination = destination_length;
+  for (size_t index_source = 0; index_source < source_length; index_source++) {
+    (*destination)[index_destination++] = source[index_source];
   }
-  for (size_t index_string2 = 0; index_string2 < string2_length; index_string2++) {
-    result[index_string1 + index_string2] = string2[index_string2];
-  }
-  result[result_length] = '\0';
-  return result;
+  (*destination)[index_destination] = '\0';
 }
 
 bool string_get_has_unique_characters(const string_t string) {
@@ -320,10 +316,9 @@ string_t string_get_formatted_number(const long long number, string_t separator)
   result[formatted_length] = '\0';
   string_reverse(result);
   if (is_negative) {
-    string_t dash = convert_character_to_string('-');
-    string_t negative_result = string_concatenate(dash, result);
+    string_t negative_result = convert_character_to_string('-');
+    string_concatenate(&negative_result, result);
     free(result);
-    free(dash);
     return negative_result;
   }
   return result;
diff --git a/lib/string.h b/lib/string.h
index afc6efa..3b241bd 100644
--- a/lib/string.h
+++ b/lib/string.h
@@ -160,11 +160,13 @@ string_t string_join(string_t* array, const char separator, size_t array_length)
 /**
  * @brief Concatenate two strings.
  *
- * @param string1
- * @param string2
+ * NOTE: Mutates the string `destination`.
+ *
+ * @param destination
+ * @param source
  * @since v1.0.0
  */
-string_t string_concatenate(string_t string1, string_t string2);
+void string_concatenate(string_t* destination, string_t source);
 
 /**
  * @brief Check if a string contains only unique characters.
diff --git a/set_version.c b/set_version.c
index 79d831c..e333b17 100644
--- a/set_version.c
+++ b/set_version.c
@@ -3,16 +3,16 @@
 
 #include "libcproject.h"
 
-int main(int argc, string_t* argv) {
+int main(int argc, char** argv) {
   if (argc != 2) {
     fprintf(stderr, "Usage: %s <version>\n", argv[0]);
     return EXIT_FAILURE;
   }
-  string_t content = "#ifndef __LIBCPROJECT_VERSION__\n";
-  content = string_concatenate(content, "#define __LIBCPROJECT_VERSION__ \"");
-  content = string_concatenate(content, argv[1]);
-  content = string_concatenate(content, "\"\n\n");
-  content = string_concatenate(content, "#endif\n");
+  string_t content = string_copy("#ifndef __LIBCPROJECT_VERSION__\n");
+  string_concatenate(&content, "#define __LIBCPROJECT_VERSION__ \"");
+  string_concatenate(&content, argv[1]);
+  string_concatenate(&content, "\"\n\n");
+  string_concatenate(&content, "#endif\n");
   int result = filesystem_write("./version.h", (byte_t*)content, string_get_length(content));
   if (result == -1) {
     fprintf(stderr, "Error: Could not write to file.\n");
diff --git a/test/string_test.c b/test/string_test.c
index da54507..47c8444 100644
--- a/test/string_test.c
+++ b/test/string_test.c
@@ -158,12 +158,14 @@ void string_join_test() {
 }
 
 void string_concatenate_test() {
-  char* result = string_concatenate("abc", "def");
+  string_t result = string_copy("abc");
+  string_concatenate(&result, "def");
   assert(assert_string_equal(result, "abcdef"));
   free(result);
 
-  result = string_concatenate("abc", "  defghi");
-  assert(assert_string_equal(result, "abc  defghi"));
+  result = string_copy("abcz");
+  string_concatenate(&result, "  defghi");
+  assert(assert_string_equal(result, "abcz  defghi"));
   free(result);
 }