diff --git a/px/px_process.py b/px/px_process.py
index fe65aba..6885f1d 100644
--- a/px/px_process.py
+++ b/px/px_process.py
@@ -91,7 +91,7 @@ def __init__(
         memory_percent: Optional[float] = None,
         cpu_percent: Optional[float] = None,
         cpu_time: Optional[float] = None,
-        aggregated_cpu_time: Optional[float] = None,
+        aggregated_cpu_time: float = 0.0,
     ) -> None:
         self.pid: int = pid
         self.ppid: Optional[int] = ppid
@@ -178,12 +178,9 @@ def set_cpu_time_seconds(self, seconds: Optional[float]) -> None:
             self.cpu_time_s = seconds_to_str(seconds)
             self.cpu_time_seconds = seconds
 
-    def set_aggregated_cpu_time_seconds(self, seconds: Optional[float]) -> None:
-        self.aggregated_cpu_time_s: str = "--"
-        self.aggregated_cpu_time_seconds = None
-        if seconds is not None:
-            self.aggregated_cpu_time_s = seconds_to_str(seconds)
-            self.aggregated_cpu_time_seconds = seconds
+    def set_aggregated_cpu_time_seconds(self, seconds: float) -> None:
+        self.aggregated_cpu_time_s = seconds_to_str(seconds)
+        self.aggregated_cpu_time_seconds = seconds
 
     def match(self, string, require_exact_user=True):
         """
diff --git a/px/px_terminal.py b/px/px_terminal.py
index 0cce65e..8194bde 100644
--- a/px/px_terminal.py
+++ b/px/px_terminal.py
@@ -409,9 +409,9 @@ def to_screen_lines(
         if sort_order == px_sort_order.SortOrder.AGGREGATED_CPU:
             if proc.pid <= 1:
                 # Both the kernel (PID 0) and the init process (PID 1) will just
-                # have contain the total time of all other processes. Since we
-                # only use this max value for highlighting (see below), if we
-                # include these only they will be highlighted. So we skip them.
+                # contain the total time of all other processes. Since we only
+                # use this max value for highlighting (see below), if we include
+                # these only they will be highlighted. So we skip them.
                 continue
             cpu_time_seconds = proc.aggregated_cpu_time_seconds
         if cpu_time_seconds is not None and cpu_time_seconds > max_cpu_time_seconds:
diff --git a/px/px_top.py b/px/px_top.py
index 835ace8..df1b6b1 100644
--- a/px/px_top.py
+++ b/px/px_top.py
@@ -126,13 +126,6 @@ def get_notnone_cpu_time_seconds(proc: px_process.PxProcess) -> float:
     return 0
 
 
-def get_notnone_aggregated_cpu_time_seconds(proc: px_process.PxProcess) -> float:
-    seconds = proc.aggregated_cpu_time_seconds
-    if seconds is not None:
-        return seconds
-    return 0
-
-
 def get_notnone_memory_percent(proc: px_process.PxProcess) -> float:
     percent = proc.memory_percent
     if percent is not None:
@@ -174,7 +167,9 @@ def sort_by_cpu_usage_tree(
 
     def sort_children(proc: px_process.PxProcess) -> None:
         proc.children = sorted(
-            proc.children, key=get_notnone_aggregated_cpu_time_seconds, reverse=True
+            proc.children,
+            key=lambda child: child.aggregated_cpu_time_seconds,
+            reverse=True,
         )
         for child in proc.children:
             sort_children(child)