diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7be4e6fa..3778ff93 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,10 @@ All versions prior to 0.0.9 are untracked.
 
 ### Fixed
 
+* Fixed bug with the `--fix` flag where new requirements were sometimes being
+  appended to requirement files instead of patching the existing requirement
+  ([#577](https://github.com/pypa/pip-audit/pull/577))
+
 * Fixed a crash caused by auditing requirements files that refer to other
   requirements files ([#568](https://github.com/pypa/pip-audit/pull/568))
 
diff --git a/pip_audit/_dependency_source/requirement.py b/pip_audit/_dependency_source/requirement.py
index 63d0b1c5..33c9993f 100644
--- a/pip_audit/_dependency_source/requirement.py
+++ b/pip_audit/_dependency_source/requirement.py
@@ -14,6 +14,7 @@
 from typing import IO, Iterator
 
 from packaging.specifiers import SpecifierSet
+from packaging.utils import canonicalize_name
 from pip_requirements_parser import InstallRequirement, InvalidRequirementLine, RequirementsFile
 
 from pip_audit._dependency_source import DependencyFixError, DependencySource, DependencySourceError
@@ -203,7 +204,10 @@ def _fix_file(self, filename: Path, fix_version: ResolvedFixVersion) -> None:
         with filename.open("w") as f:
             found = False
             for req in reqs:
-                if isinstance(req, InstallRequirement) and req.name == fix_version.dep.name:
+                if (
+                    isinstance(req, InstallRequirement)
+                    and canonicalize_name(req.name) == fix_version.dep.canonical_name
+                ):
                     found = True
                     if req.specifier.contains(
                         fix_version.dep.version
diff --git a/test/dependency_source/test_requirement.py b/test/dependency_source/test_requirement.py
index 1eeee699..a5ac69ad 100644
--- a/test/dependency_source/test_requirement.py
+++ b/test/dependency_source/test_requirement.py
@@ -198,6 +198,52 @@ def test_requirement_source_fix(req_file):
     )
 
 
+def test_requirement_source_fix_roundtrip(req_file):
+    req_path = req_file()
+    with open(req_path, "w") as f:
+        f.write("flask==0.5")
+
+    source = requirement.RequirementSource([req_path])
+    specs = list(source.collect())
+
+    flask_dep: ResolvedDependency | None = None
+    for spec in specs:
+        if isinstance(spec, ResolvedDependency) and spec.canonical_name == "flask":
+            flask_dep = spec
+            break
+    assert flask_dep is not None
+    assert flask_dep == ResolvedDependency(name="Flask", version=Version("0.5"))
+
+    flask_fix = ResolvedFixVersion(dep=flask_dep, version=Version("1.0"))
+    source.fix(flask_fix)
+
+    with open(req_path) as f:
+        assert f.read().strip() == "flask==1.0"
+
+
+def test_requirement_source_fix_roundtrip_non_canonical_name(req_file):
+    req_path = req_file()
+    with open(req_path, "w") as f:
+        f.write("Flask==0.5")
+
+    source = requirement.RequirementSource([req_path])
+    specs = list(source.collect())
+
+    flask_dep: ResolvedDependency | None = None
+    for spec in specs:
+        if isinstance(spec, ResolvedDependency) and spec.canonical_name == "flask":
+            flask_dep = spec
+            break
+    assert flask_dep is not None
+    assert flask_dep == ResolvedDependency(name="Flask", version=Version("0.5"))
+
+    flask_fix = ResolvedFixVersion(dep=flask_dep, version=Version("1.0"))
+    source.fix(flask_fix)
+
+    with open(req_path) as f:
+        assert f.read().strip() == "Flask==1.0"
+
+
 def test_requirement_source_fix_multiple_files(req_file):
     _check_fixes(
         ["flask==0.5", "requests==2.0\nflask==0.5"],