diff --git a/include/haproxy/tools.h b/include/haproxy/tools.h
index 3726f6353..d76b2d13c 100644
--- a/include/haproxy/tools.h
+++ b/include/haproxy/tools.h
@@ -399,11 +399,11 @@ int addr_is_local(const struct netns_entry *ns,
  * <map> with the hexadecimal representation of their ASCII-code (2 digits)
  * prefixed by <escape>, and will store the result between <start> (included)
  * and <stop> (excluded), and will always terminate the string with a '\0'
- * before <stop>. The position of the '\0' is returned if the conversion
- * completes. If bytes are missing between <start> and <stop>, then the
- * conversion will be incomplete and truncated. If <stop> <= <start>, the '\0'
- * cannot even be stored so we return <start> without writing the 0.
+ * before <stop>. If bytes are missing between <start> and <stop>, then the
+ * conversion will be incomplete and truncated.
  * The input string must also be zero-terminated.
+ *
+ * Return the address of the \0 character, or NULL on error
  */
 extern const char hextab[];
 extern long query_encode_map[];
@@ -424,8 +424,9 @@ char *encode_chunk(char *start, char *stop,
  * is reached or NULL-byte is encountered. The result will
  * be stored between <start> (included) and <stop> (excluded). This
  * function will always try to terminate the resulting string with a '\0'
- * before <stop>, and will return its position if the conversion
- * completes.
+ * before <stop>.
+ *
+ * Return the address of the \0 character, or NULL on error
  */
 char *escape_string(char *start, char *stop,
 		    const char escape, const long *map,
diff --git a/src/log.c b/src/log.c
index a1236e9f2..847706d2c 100644
--- a/src/log.c
+++ b/src/log.c
@@ -1734,6 +1734,8 @@ int get_log_facility(const char *fac)
  * When using the +E log format option, it will try to escape '"\]'
  * characters with '\' as prefix. The same prefix should not be used as
  * <escape>.
+ *
+ * Return the address of the \0 character, or NULL on error
  */
 static char *lf_encode_string(char *start, char *stop,
                               const char escape, const long *map,
@@ -1764,13 +1766,14 @@ static char *lf_encode_string(char *start, char *stop,
 				string++;
 			}
 			*start = '\0';
+			return start;
 		}
 	}
 	else {
 		return encode_string(start, stop, escape, map, string);
 	}
 
-	return start;
+	return NULL;
 }
 
 /*
@@ -1779,6 +1782,8 @@ static char *lf_encode_string(char *start, char *stop,
  * When using the +E log format option, it will try to escape '"\]'
  * characters with '\' as prefix. The same prefix should not be used as
  * <escape>.
+ *
+ * Return the address of the \0 character, or NULL on error
  */
 static char *lf_encode_chunk(char *start, char *stop,
                              const char escape, const long *map,
@@ -1814,13 +1819,14 @@ static char *lf_encode_chunk(char *start, char *stop,
 				str++;
 			}
 			*start = '\0';
+			return start;
 		}
 	}
 	else {
 		return encode_chunk(start, stop, escape, map, chunk);
 	}
 
-	return start;
+	return NULL;
 }
 
 /*
diff --git a/src/tools.c b/src/tools.c
index 475922283..b08fb18ce 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -1969,11 +1969,11 @@ int addr_is_local(const struct netns_entry *ns,
  * <map> with the hexadecimal representation of their ASCII-code (2 digits)
  * prefixed by <escape>, and will store the result between <start> (included)
  * and <stop> (excluded), and will always terminate the string with a '\0'
- * before <stop>. The position of the '\0' is returned if the conversion
- * completes. If bytes are missing between <start> and <stop>, then the
- * conversion will be incomplete and truncated. If <stop> <= <start>, the '\0'
- * cannot even be stored so we return <start> without writing the 0.
+ * before <stop>. If bytes are missing between <start> and <stop>, then the
+ * conversion will be incomplete and truncated.
  * The input string must also be zero-terminated.
+ *
+ * Return the address of the \0 character, or NULL on error
  */
 const char hextab[16] = "0123456789ABCDEF";
 char *encode_string(char *start, char *stop,
@@ -1995,8 +1995,9 @@ char *encode_string(char *start, char *stop,
 			string++;
 		}
 		*start = '\0';
+		return start;
 	}
-	return start;
+	return NULL;
 }
 
 /*
@@ -2025,8 +2026,9 @@ char *encode_chunk(char *start, char *stop,
 			str++;
 		}
 		*start = '\0';
+		return start;
 	}
-	return start;
+	return NULL;
 }
 
 /*
@@ -2035,8 +2037,9 @@ char *encode_chunk(char *start, char *stop,
  * is reached or NULL-byte is encountered. The result will
  * be stored between <start> (included) and <stop> (excluded). This
  * function will always try to terminate the resulting string with a '\0'
- * before <stop>, and will return its position if the conversion
- * completes.
+ * before <stop>.
+ *
+ * Return the address of the \0 character, or NULL on error
  */
 char *escape_string(char *start, char *stop,
 		    const char escape, const long *map,
@@ -2056,8 +2059,9 @@ char *escape_string(char *start, char *stop,
 			string++;
 		}
 		*start = '\0';
+		return start;
 	}
-	return start;
+	return NULL;
 }
 
 /* Check a string for using it in a CSV output format. If the string contains