diff --git a/doc/starting.rst b/doc/starting.rst
index c55edeb9..5f24f815 100644
--- a/doc/starting.rst
+++ b/doc/starting.rst
@@ -87,8 +87,7 @@ the terminal size:
 #. ``PUDB_TERM_SIZE`` environment variable
 #. Size of the terminal in which the debugged program is running
    (as returned by ``os.get_terminal_size()``)
-#. Default fallback value of ``(80, 20)`` if one of the previous steps
-   fails with an exception
+#. Default fallback value of ``(80, 20)``
 
 At this point, the debugger will look for a free port and wait for a telnet
 connection::
diff --git a/pudb/forked.py b/pudb/forked.py
index 66ae091c..d8ac88ad 100644
--- a/pudb/forked.py
+++ b/pudb/forked.py
@@ -14,15 +14,18 @@ def set_trace(paused=True, frame=None, term_size=None):
     if frame is None:
         frame = sys._getframe().f_back
     if term_size is None:
-        try:
-            term_size = os.environ.get("PUDB_TERM_SIZE", "")
+        term_size = os.environ.get("PUDB_TERM_SIZE")
+        if term_size is not None:
             term_size = tuple(map(int, term_size.split("x")))
             if len(term_size) != 2:
+                raise ValueError("PUDB_TERM_SIZE should have two dimensions")
+        else:
+            try:
                 # Getting terminal size
                 s = os.get_terminal_size()
                 term_size = (s.columns, s.lines)
-        except Exception:
-            term_size = (80, 24)
+            except Exception:
+                term_size = (80, 24)
 
     Debugger(
         stdin=open("/dev/stdin"),
diff --git a/pudb/remote.py b/pudb/remote.py
index ee6adea4..373424cb 100644
--- a/pudb/remote.py
+++ b/pudb/remote.py
@@ -45,15 +45,13 @@
 
 from pudb.debugger import Debugger
 
-__all__ = ["PUDB_RDB_HOST", "PUDB_RDB_PORT", "PUDB_TERM_SIZE",
-           "default_port", "debugger", "set_trace",
+__all__ = ["PUDB_RDB_HOST", "PUDB_RDB_PORT", "default_port", "debugger", "set_trace",
            "debug_remote_on_single_rank"]
 
 default_port = 6899
 
 PUDB_RDB_HOST = os.environ.get("PUDB_RDB_HOST") or "127.0.0.1"
 PUDB_RDB_PORT = int(os.environ.get("PUDB_RDB_PORT") or default_port)
-PUDB_TERM_SIZE = os.environ.get("PUDB_TERM_SIZE", "")
 
 #: Holds the currently active debugger.
 _current = [None]
@@ -140,13 +138,17 @@ def __init__(
         self.out = out
 
         if term_size is None:
-            try:
-                term_size = tuple(map(int, PUDB_TERM_SIZE.split("x")))
+            term_size = os.environ.get("PUDB_TERM_SIZE")
+            if term_size is not None:
+                term_size = tuple(map(int, term_size.split("x")))
                 if len(term_size) != 2:
+                    raise ValueError("PUDB_TERM_SIZE should have two dimensions")
+            else:
+                try:
                     s = os.get_terminal_size()
                     term_size = (s.columns, s.lines)
-            except Exception:
-                term_size = (80, 24)
+                except Exception:
+                    term_size = (80, 24)
 
         self._prev_handles = sys.stdin, sys.stdout
         self._client, (address, port) = self.get_client(