diff --git a/numba_cuda/numba/cuda/misc/firstlinefinder.py b/numba_cuda/numba/cuda/misc/firstlinefinder.py
index de77112c6..16daf889a 100644
--- a/numba_cuda/numba/cuda/misc/firstlinefinder.py
+++ b/numba_cuda/numba/cuda/misc/firstlinefinder.py
@@ -7,6 +7,8 @@
 """
 
 import ast
+import inspect
+import textwrap
 
 
 class FindDefFirstLine(ast.NodeVisitor):
@@ -16,17 +18,23 @@ class FindDefFirstLine(ast.NodeVisitor):
     first_stmt_line : int or None
         This stores the first statement line number if the definition is found.
         Or, ``None`` if the definition is not found.
+    def_lineno : int or None
+        This stores the 'def' line number if the definition is found.
+        Or, ``None`` if the definition is not found.
     """
 
-    def __init__(self, code):
+    def __init__(self, name, firstlineno):
         """
         Parameters
         ----------
-        code :
-            The function's code object.
+        name : str
+            The function's name (co_name).
+        firstlineno : int
+            The function's first line number (co_firstlineno), adjusted for
+            any offset if the source is a fragment.
         """
-        self._co_name = code.co_name
-        self._co_firstlineno = code.co_firstlineno
+        self._co_name = name
+        self._co_firstlineno = firstlineno
         self.first_stmt_line = None
         self.def_lineno = None
 
@@ -76,8 +84,11 @@ def _is_docstring(node):
 
 def get_func_body_first_lineno(pyfunc):
     """
-    Look up the first line of function body using the file in
-    ``pyfunc.__code__.co_filename``.
+    Look up the first line of function body.
+
+    Uses inspect.getsourcelines() which works for both regular .py files
+    (via linecache reading from disk) and Jupyter notebook cells (via
+    IPython's linecache registration).
 
     Returns
     -------
@@ -87,21 +98,29 @@ def get_func_body_first_lineno(pyfunc):
     """
     co = pyfunc.__code__
     try:
-        with open(co.co_filename) as fin:
-            file_content = fin.read()
-    except (FileNotFoundError, OSError):
-        return
+        lines, offset = inspect.getsourcelines(pyfunc)
+        source = "".join(lines)
+        offset = offset - 1
+    except (OSError, TypeError):
+        return None
+
+    tree = ast.parse(textwrap.dedent(source))
+    finder = FindDefFirstLine(co.co_name, co.co_firstlineno - offset)
+    finder.visit(tree)
+    if finder.first_stmt_line:
+        return finder.first_stmt_line + offset
     else:
-        tree = ast.parse(file_content)
-        finder = FindDefFirstLine(co)
-        finder.visit(tree)
-        return finder.first_stmt_line
+        # No first line found.
+        return None
 
 
 def get_func_def_lineno(pyfunc):
     """
-    Look up the line number of the function definition ('def' line) using
-    the file in ``pyfunc.__code__.co_filename``.
+    Look up the line number of the function definition ('def' line).
+
+    Uses inspect.getsourcelines() which works for both regular .py files
+    (via linecache reading from disk) and Jupyter notebook cells (via
+    IPython's linecache registration).
 
     Returns
     -------
@@ -111,12 +130,17 @@ def get_func_def_lineno(pyfunc):
     """
     co = pyfunc.__code__
     try:
-        with open(co.co_filename) as fin:
-            file_content = fin.read()
-    except (FileNotFoundError, OSError):
-        return
+        lines, offset = inspect.getsourcelines(pyfunc)
+        source = "".join(lines)
+        offset = offset - 1
+    except (OSError, TypeError):
+        return None
+
+    tree = ast.parse(textwrap.dedent(source))
+    finder = FindDefFirstLine(co.co_name, co.co_firstlineno - offset)
+    finder.visit(tree)
+    if finder.def_lineno:
+        return finder.def_lineno + offset
     else:
-        tree = ast.parse(file_content)
-        finder = FindDefFirstLine(co)
-        finder.visit(tree)
-        return finder.def_lineno
+        # No def line found.
+        return None
diff --git a/numba_cuda/numba/cuda/tests/cudapy/test_debuginfo.py b/numba_cuda/numba/cuda/tests/cudapy/test_debuginfo.py
index 4f1388424..721eb8003 100644
--- a/numba_cuda/numba/cuda/tests/cudapy/test_debuginfo.py
+++ b/numba_cuda/numba/cuda/tests/cudapy/test_debuginfo.py
@@ -626,6 +626,65 @@ def foo():
         # and refers to the offending function
         self.assertIn(str(foo.py_func), msg)
 
+    def test_linecache_source(self):
+        """Test that source from linecache (like Jupyter notebooks) works.
+
+        This simulates how Jupyter/IPython registers cell source in linecache,
+        allowing inspect.getsourcelines() to find it even though the file
+        doesn't exist on disk. Fixes issue #721.
+        """
+        import linecache
+
+        # Source with a multi-line decorator
+        strsrc = dedent("""
+        @cuda.jit(
+            "void(int32[:])",
+            debug=True,
+            opt=False
+        )
+        def foo(x):
+            x[0] = 1
+        """).strip()
+
+        # Simulate Jupyter by registering source in linecache
+        fake_filename = "<ipython-input-test-linecache>"
+        lines = [line + "\n" for line in strsrc.splitlines()]
+        linecache.cache[fake_filename] = (
+            len(strsrc),
+            None,  # mtime=None means never expire
+            lines,
+            fake_filename,
+        )
+
+        try:
+            # Compile and execute using the fake filename
+            code = compile(strsrc, fake_filename, "exec")
+            exec_globals = {"cuda": cuda}
+            exec(code, exec_globals)
+            foo = exec_globals["foo"]
+
+            # Should NOT produce a warning since source is in linecache
+            with warnings.catch_warnings(record=True) as w:
+                warnings.simplefilter("always", NumbaDebugInfoWarning)
+                ignore_internal_warnings()
+                foo[1, 1](cuda.to_device(np.zeros(1, dtype=np.int32)))
+
+            # Filter for NumbaDebugInfoWarning specifically
+            debug_warnings = [
+                x for x in w if x.category == NumbaDebugInfoWarning
+            ]
+            self.assertEqual(
+                len(debug_warnings),
+                0,
+                msg=f"Unexpected warning: {debug_warnings}",
+            )
+
+            # Verify debug info is present in the PTX
+            self._check(foo, sig=(types.int32[:],), expect=True)
+        finally:
+            # Clean up linecache
+            linecache.cache.pop(fake_filename, None)
+
     def test_no_if_op_bools_declared(self):
         @cuda.jit(
             "int64(boolean, boolean)",