diff --git a/src/ivoc/strfun.cpp b/src/ivoc/strfun.cpp
index 4c1358fa50..cb5375eb82 100644
--- a/src/ivoc/strfun.cpp
+++ b/src/ivoc/strfun.cpp
@@ -91,7 +91,11 @@ static double l_tail(void*) {
 
 static double l_ltrim(void*) {
     std::string s(gargstr(1));
-    s.erase(0, s.find_first_not_of(" \r\n\t\f\v"));
+    std::string chars = " \r\n\t\f\v";
+    if (ifarg(3)) {
+        chars = gargstr(3);
+    }
+    s.erase(0, s.find_first_not_of(chars));
 
     char** ret = hoc_pgargstr(2);
     hoc_assign_str(ret, s.c_str());
@@ -100,7 +104,11 @@ static double l_ltrim(void*) {
 
 static double l_rtrim(void*) {
     std::string s(gargstr(1));
-    s.erase(s.find_last_not_of(" \r\n\t\f\v") + 1);
+    std::string chars = " \r\n\t\f\v";
+    if (ifarg(3)) {
+        chars = gargstr(3);
+    }
+    s.erase(s.find_last_not_of(chars) + 1);
 
     char** ret = hoc_pgargstr(2);
     hoc_assign_str(ret, s.c_str());
diff --git a/test/unit_tests/hoc_python/test_StringFunctions.py b/test/unit_tests/hoc_python/test_StringFunctions.py
index 0cfcb44dc4..ecea51955d 100644
--- a/test/unit_tests/hoc_python/test_StringFunctions.py
+++ b/test/unit_tests/hoc_python/test_StringFunctions.py
@@ -55,6 +55,26 @@ def test_tail():
     assert tail[0] == ""
 
 
+def text_rtrim():
+    text = "bar\t; \t\n"
+    out = h.ref("")
+    sf.rtrim(text, out)
+    assert out[0] == "bar\t;"
+
+    sf.rtrim(text, out, " \t\n\f\v\r;")
+    assert out[0] == "bar"
+
+
+def test_ltrim():
+    text = "  \t \n# foo"
+    out = h.ref("")
+    sf.ltrim(text, out)
+    assert out[0] == "# foo"
+
+    sf.ltrim(text, out, " \t\n\f\r\v#")
+    assert out[0] == "foo"
+
+
 def test_right():
     s = h.ref("foobarshi")
     sf.right(s, 6)