diff --git a/Lib/configparser.py b/Lib/configparser.py
--- a/Lib/configparser.py
+++ b/Lib/configparser.py
@@ -406,7 +406,9 @@
         rawval = parser.get(section, option, raw=True, fallback=rest)
         if depth > MAX_INTERPOLATION_DEPTH:
             raise InterpolationDepthError(option, section, rawval)
-        while rest:
+        _rest = rest
+        del rest
+        for rest in _rest:
             p = rest.find("%")
             if p < 0:
                 accum.append(rest)
@@ -467,7 +469,9 @@
         rawval = parser.get(section, option, raw=True, fallback=rest)
         if depth > MAX_INTERPOLATION_DEPTH:
             raise InterpolationDepthError(option, section, rawval)
-        while rest:
+        _rest = rest
+        del rest
+        for rest in _rest:
             p = rest.find("$")
             if p < 0:
                 accum.append(rest)