diff --git a/src/clj_jtwig/standard_functions.clj b/src/clj_jtwig/standard_functions.clj
index 1e1a70e..d012c67 100644
--- a/src/clj_jtwig/standard_functions.clj
+++ b/src/clj_jtwig/standard_functions.clj
@@ -50,14 +50,14 @@
    {:fn (fn [coll value]
           (cond
             (instance? java.util.List coll) (.indexOf coll value)
-            (string? coll)                  (.indexOf coll value)
+            (string? coll)                  (.indexOf coll (if (char? value) (int value) value))
             :else                           (throw (new Exception (str "'index_if' passed invalid collection type: " (type coll))))))}
 
    "last_index_of"
    {:fn (fn [coll value]
           (cond
             (instance? java.util.List coll) (.lastIndexOf coll value)
-            (string? coll)                  (.lastIndexOf coll value)
+            (string? coll)                  (.lastIndexOf coll (if (char? value) (int value) value))
             :else                           (throw (new Exception (str "'last_index_if' passed invalid collection type: " (type coll))))))}
 
    "max"