diff --git a/manimlib/mobject/svg/mtex_mobject.py b/manimlib/mobject/svg/mtex_mobject.py
index 10d3989e..f0586904 100644
--- a/manimlib/mobject/svg/mtex_mobject.py
+++ b/manimlib/mobject/svg/mtex_mobject.py
@@ -135,17 +135,17 @@ class MTex(LabelledString):
             if span_begin in brace_indices_dict.keys():
                 span_end = brace_indices_dict[span_begin] + 1
             else:
-                span = self.find_spans(script_pattern, pos=span_begin)[0]
-                if span[0] != span_begin:
+                spans = self.find_spans(script_pattern, pos=span_begin)
+                if not spans or spans[0][0] != span_begin:
                     script_name = {
                         "_": "subscript",
                         "^": "superscript"
-                    }[script_char]
+                    }[self.get_string(char_span)]
                     raise ValueError(
                         f"Unclear {script_name} detected while parsing. "
                         "Please use braces to clarify"
                     )
-                span_end = span[1]
+                span_end = spans[0][1]
             result.append((span_begin, span_end))
         return result