diff --git a/slurm-eff-tool.py b/slurm-eff-tool.py
index 17168e3..8a9298b 100755
--- a/slurm-eff-tool.py
+++ b/slurm-eff-tool.py
@@ -636,15 +636,15 @@ def format_seconds(seconds: int | float | None) -> str:
     return f"{hours:02d}:{minutes:02d}:{sec:02d}"
 
 def format_hours(hours: float | None) -> str:
-    """Return string representation in format hours:seconds"""
+    """Return string representation in format hours:minutes:seconds."""
     if hours is None:
         return "Unknown"
-    td = timedelta(hours)
+    td = timedelta(hours=hours)
     sraw = int(td.total_seconds())
     hr = sraw // 3600
     mn = (sraw % 3600) // 60
     sc = sraw % 60
-    return f"{hr}:{round(mn,0)}:{sc}"
+    return f"{hr}:{round(mn,0):02d}:{sc:02d}"
 
 
 def parse_size_to_bytes(value: str) -> int | None: