diff --git a/Lib/textwrap.py b/Lib/textwrap.py
index bb6a1186316275..7aa2a82af2fcc3 100644
--- a/Lib/textwrap.py
+++ b/Lib/textwrap.py
@@ -432,15 +432,30 @@ def dedent(text):
     lines = text.split('\n')
 
     # Get length of leading whitespace, inspired by ``os.path.commonprefix()``.
-    non_blank_lines = [l for l in lines if l and not l.isspace()]
-    l1 = min(non_blank_lines, default='')
-    l2 = max(non_blank_lines, default='')
-    margin = 0
+    val = False
+    for i, line in enumerate(lines):
+        # Compute min + max concurrently + normalize others
+        if line and not line.isspace():
+            if val:
+                if line < l1:
+                    l1 = line
+                elif line > l2:
+                    l2 = line
+            else:
+               val = True
+               l1 = l2 = line 
+                
+        else:
+            lines[i] = ''
+    
+    if not val or not l1:
+        return '\n'.join(lines)
+    
     for margin, c in enumerate(l1):
         if c != l2[margin] or c not in ' \t':
             break
 
-    return '\n'.join([l[margin:] if not l.isspace() else '' for l in lines])
+    return '\n'.join([line[margin:] for line in lines])
 
 
 def indent(text, prefix, predicate=None):