diff --git a/freqtrade/strategy/interface.py b/freqtrade/strategy/interface.py
index e80ee0e0e..887c1d583 100644
--- a/freqtrade/strategy/interface.py
+++ b/freqtrade/strategy/interface.py
@@ -58,6 +58,9 @@ class IStrategy(ABC):
         ticker_interval -> str: value of the ticker interval to use for the strategy
     """
 
+    _populate_fun_len: int = 0
+    _buy_fun_len: int = 0
+    _sell_fun_len: int = 0
     # associated minimal roi
     minimal_roi: Dict
 
@@ -283,7 +286,7 @@ class IStrategy(ABC):
         :param pair: The currently traded pair
         :return: a Dataframe with all mandatory indicators for the strategies
         """
-        if len(self.populate_indicators.__annotations__) == 2:
+        if self._populate_fun_len == 2:
             warnings.warn("deprecated - check out the Sample strategy to see "
                           "the current function headers!", DeprecationWarning)
             return self.populate_indicators(dataframe)  # type: ignore
@@ -298,7 +301,7 @@ class IStrategy(ABC):
         :param pair: The currently traded pair
         :return: DataFrame with buy column
         """
-        if len(self.populate_buy_trend.__annotations__) == 2:
+        if self._buy_fun_len == 2:
             warnings.warn("deprecated - check out the Sample strategy to see "
                           "the current function headers!", DeprecationWarning)
             return self.populate_buy_trend(dataframe)  # type: ignore
@@ -313,7 +316,7 @@ class IStrategy(ABC):
         :param pair: The currently traded pair
         :return: DataFrame with sell column
         """
-        if len(self.populate_sell_trend.__annotations__) == 2:
+        if self._sell_fun_len == 2:
             warnings.warn("deprecated - check out the Sample strategy to see "
                           "the current function headers!", DeprecationWarning)
             return self.populate_sell_trend(dataframe)  # type: ignore
diff --git a/freqtrade/strategy/resolver.py b/freqtrade/strategy/resolver.py
index 3360cd44a..ea887e43e 100644
--- a/freqtrade/strategy/resolver.py
+++ b/freqtrade/strategy/resolver.py
@@ -92,6 +92,13 @@ class StrategyResolver(object):
                 strategy = self._search_strategy(path, strategy_name=strategy_name, config=config)
                 if strategy:
                     logger.info('Using resolved strategy %s from \'%s\'', strategy_name, path)
+                    strategy._populate_fun_len = len(
+                        inspect.getfullargspec(strategy.populate_indicators).args)
+                    strategy._buy_fun_len = len(
+                        inspect.getfullargspec(strategy.populate_buy_trend).args)
+                    strategy._sell_fun_len = len(
+                        inspect.getfullargspec(strategy.populate_sell_trend).args)
+
                     return import_strategy(strategy, config=config)
             except FileNotFoundError:
                 logger.warning('Path "%s" does not exist', path)
diff --git a/freqtrade/tests/strategy/test_strategy.py b/freqtrade/tests/strategy/test_strategy.py
index c90271506..02eea312f 100644
--- a/freqtrade/tests/strategy/test_strategy.py
+++ b/freqtrade/tests/strategy/test_strategy.py
@@ -199,15 +199,9 @@ def test_call_deprecated_function(result, monkeypatch):
     pair = 'ETH/BTC'
 
     # Make sure we are using a legacy function
-    assert len(resolver.strategy.populate_indicators.__annotations__) == 2
-    assert 'dataframe' in resolver.strategy.populate_indicators.__annotations__
-    assert 'pair' not in resolver.strategy.populate_indicators.__annotations__
-    assert len(resolver.strategy.populate_buy_trend.__annotations__) == 2
-    assert 'dataframe' in resolver.strategy.populate_buy_trend.__annotations__
-    assert 'pair' not in resolver.strategy.populate_buy_trend.__annotations__
-    assert len(resolver.strategy.populate_sell_trend.__annotations__) == 2
-    assert 'dataframe' in resolver.strategy.populate_sell_trend.__annotations__
-    assert 'pair' not in resolver.strategy.populate_sell_trend.__annotations__
+    assert resolver.strategy._populate_fun_len == 2
+    assert resolver.strategy._buy_fun_len == 2
+    assert resolver.strategy._sell_fun_len == 2
 
     indicator_df = resolver.strategy.advise_indicators(result, pair=pair)
     assert type(indicator_df) is DataFrame