diff --git a/Lib/inspect.py b/Lib/inspect.py
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -888,6 +888,15 @@
         pass
     return lines[:blockfinder.last]
 
+def _line_number_helper(code_obj, lines, lnum):
+    """Return a list of source lines and starting line number for a code object.
+
+    The arguments must be a code object with lines and lnum from findsource.
+    """
+    line_offsets = list(code_obj.co_lnotab[1::2])
+    end_line = sum(line_offsets) + lnum + 1
+    return lines[lnum:end_line], lnum + 1
+
 def getsourcelines(object):
     """Return a list of source lines and starting line number for an object.
 
@@ -899,8 +908,16 @@
     object = unwrap(object)
     lines, lnum = findsource(object)
 
-    if ismodule(object): return lines, 0
-    else: return getblock(lines[lnum:]), lnum + 1
+    if ismodule(object):
+        return lines, 0
+    elif iscode(object):
+        return _line_number_helper(object, lines, lnum)
+    elif isfunction(object):
+        return _line_number_helper(object.__code__, lines, lnum)
+    elif ismethod(object):
+        return _line_number_helper(object.__func__.__code__, lines, lnum)
+    else:
+        return getblock(lines[lnum:]), lnum + 1
 
 def getsource(object):
     """Return the text of the source code for an object.
diff --git a/Lib/test/inspect_fodder2.py b/Lib/test/inspect_fodder2.py
--- a/Lib/test/inspect_fodder2.py
+++ b/Lib/test/inspect_fodder2.py
@@ -110,6 +110,14 @@
 def keyword_only_arg(*, arg):
     pass
 
+@wrap(lambda: None)
+def func114():
+    return 115
+
+class ClassWithMethod:
+    def method(self):
+        pass
+
 from functools import wraps
 
 def decorator(func):
@@ -118,7 +126,7 @@
         return 42
     return fake
 
-#line 121
+#line 129
 @decorator
 def real():
     return 20
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -392,6 +392,9 @@
         finally:
             linecache.getlines = getlines
 
+    def test_getsource_on_code_object(self):
+        self.assertSourceEqual(mod.eggs.__code__, 12, 18)
+
 class TestDecorators(GetSourceBase):
     fodderModule = mod2
 
@@ -402,7 +405,10 @@
         self.assertSourceEqual(mod2.gone, 9, 10)
 
     def test_getsource_unwrap(self):
-        self.assertSourceEqual(mod2.real, 122, 124)
+        self.assertSourceEqual(mod2.real, 130, 132)
+
+    def test_decorator_with_lambda(self):
+        self.assertSourceEqual(mod2.func114, 113, 115)
 
 class TestOneliners(GetSourceBase):
     fodderModule = mod2
@@ -497,6 +503,9 @@
             self.assertRaises(IOError, inspect.findsource, co)
             self.assertRaises(IOError, inspect.getsource, co)
 
+    def test_getsource_on_method(self):
+        self.assertSourceEqual(mod2.ClassWithMethod.method, 118, 119)
+
 class TestNoEOL(GetSourceBase):
     def __init__(self, *args, **kwargs):
         self.tempdir = TESTFN + '_dir'
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -118,6 +118,9 @@
 - Issue #22117: Fix os.utime(), it now rounds the timestamp towards minus
   infinity (-inf) instead of rounding towards zero.
 
+- Issue #21217: Fix inspect.getsourcelines to correctly handle decorators
+  with lambda functions passed as arguments.
+
 Build
 -----