diff --git a/src/constants.h b/src/constants.h
index 66fe03f..f76f78f 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -27,8 +27,8 @@
 #define ENV_NAME_FORCE_WRITE "COLORED_STDERR_FORCE_WRITE"
 
 /* Strings written before/after each matched function. */
-#define DEFAULT_PRE_STRING "\e[91m"
-#define DEFAULT_POST_STRING "\e[0m"
+#define DEFAULT_PRE_STRING "\033[91m"
+#define DEFAULT_POST_STRING "\033[0m"
 
 /* Number of elements to allocate statically. Highest descriptor observed in
  * normal use was 255 (by bash), which yielded this limit to prevent