diff --git a/build_defs/python.build_defs b/build_defs/python.build_defs
index 2435ac29..97af2a5b 100644
--- a/build_defs/python.build_defs
+++ b/build_defs/python.build_defs
@@ -440,7 +440,7 @@ def pip_library(name:str, version:str, labels:list=[], hashes:list=None, package
     repo = repo or CONFIG.PYTHON.DEFAULT_PIP_REPO
     if repo:
         if looks_like_build_label(repo):  # Looks like a build label, not a URL.
-            repo_flag = f'-f %(location {repo})'
+            repo_flag = f'-f $(location {repo})'
             deps += [repo]
         else:
             repo_flag = '-f ' + repo
@@ -507,6 +507,7 @@ def pip_library(name:str, version:str, labels:list=[], hashes:list=None, package
         test_only = test_only,
         output_dirs = [pip_target_dir],
         srcs = patches if patch else [],
+        deps = [repo] if looks_like_build_label(repo) else [],
         building_description = 'Fetching...',
         tools = tools,
         sandbox = False,
@@ -516,7 +517,7 @@ def pip_library(name:str, version:str, labels:list=[], hashes:list=None, package
     # Don't include the dependency whl's into our whl. They are later picked up by py_binary anyway.
     cmd = f'$TOOLS_ARCAT z --suffix="" --exclude_suffix=whl --include_other -i . -r $PKG/{name}:$PKG'
     if not licences:
-        cmd += ' && find . -name METADATA -or -name PKG-INFO | grep -v "^./build/" | xargs grep -E "License ?:" | grep -v UNKNOWN | cat || true'
+        cmd += ' && find . -name METADATA -or -name PKG-INFO | grep -v "^./build/" | xargs grep -E "License(-Expression)? ?:" | grep -v UNKNOWN | cat || true'
 
     return build_rule(
         name = name,
@@ -661,7 +662,7 @@ def python_wheel(name:str, version:str, labels:list=[], hashes:list=None, packag
         cmd += ['find . %s | xargs rm -rf' % ' -or '.join(['-name "%s"' % s for s in strip])]
     if not licences:
         cmd += ['find . -name METADATA -or -name PKG-INFO | grep -v "^./build/" | '
-                'xargs grep -hE "License ?:" | grep -v UNKNOWN | cat || true']
+                'xargs grep -hE "License(-Expression)? ?:" | grep -v UNKNOWN | cat || true']
     if patch:
         patches, c = _patch_cmd(patch)
         cmd += c
@@ -848,6 +849,9 @@ def _add_licences(name, output):
             # section still seems to know what they are licenced as.
             add_licence(name, line.split(' :: ')[-1])
             found = True
+        elif line.startswith('License-Expression: '):
+            add_licence(name, line.removeprefix('License-Expression: '))
+            found = True
     if not found:
         name = name.lstrip('_').split('#')[0]
         msg = f'No licence found for {name}, should add licences = [...] to the rule'
diff --git a/test/BUILD b/test/BUILD
index d12cad3f..91fd408c 100644
--- a/test/BUILD
+++ b/test/BUILD
@@ -152,6 +152,14 @@ plugin_e2e_test(
     },
 )
 
+# Test that pip_library correctly auto-detects licences from a PEP 639 `License-Expression:`
+# metadata field (as well as the legacy `License:` field).
+plugin_e2e_test(
+    name = "pip_library_license_expression_test",
+    repo = "license_expression_repo",
+    test_cmd = "plz build //third_party/python:fakepkg",
+)
+
 # Test that python_wheel targets can have name_scheme as a list or a string
 
 python_test(
diff --git a/test/license_expression_repo/.plzconfig b/test/license_expression_repo/.plzconfig
new file mode 100644
index 00000000..e5f64a6a
--- /dev/null
+++ b/test/license_expression_repo/.plzconfig
@@ -0,0 +1,3 @@
+[Plugin "python"]
+Target = //plugins:python
+RequireLicences = true
diff --git a/test/license_expression_repo/plugins/BUILD_FILE b/test/license_expression_repo/plugins/BUILD_FILE
new file mode 100644
index 00000000..bd8b3fd9
--- /dev/null
+++ b/test/license_expression_repo/plugins/BUILD_FILE
@@ -0,0 +1,4 @@
+plugin_repo(
+    name = "python",
+    revision = "e2e",
+)
diff --git a/test/license_expression_repo/third_party/python/BUILD_FILE b/test/license_expression_repo/third_party/python/BUILD_FILE
new file mode 100644
index 00000000..35d639ab
--- /dev/null
+++ b/test/license_expression_repo/third_party/python/BUILD_FILE
@@ -0,0 +1,33 @@
+subinclude("///python//build_defs:python")
+
+package(
+    # The pip_library target below installs from a local wheelhouse fixture, not the network -
+    # make sure we don't accidentally try to look it up on PyPI.
+    python = {
+        "use_pypi": False,
+    },
+)
+
+# Builds a fixture wheel from plain-text sources whose METADATA only declares a PEP 639
+# `License-Expression:` field (no legacy `License:` or `Classifier: License`), to exercise
+# pip_library's auto-detection of that field.
+genrule(
+    name = "fakepkg_whl",
+    srcs = ["fakepkg_src"],
+    outs = ["fakepkg-1.0.0-py3-none-any.whl"],
+    cmd = "cd $SRC && $TOOLS_ARCAT z -d -i . -o $OUT",
+    tools = {"arcat": [CONFIG.ARCAT_TOOL]},
+)
+
+genrule(
+    name = "wheelhouse",
+    srcs = [":fakepkg_whl"],
+    cmd = "mkdir -p wheelhouse && cp $SRCS wheelhouse/",
+    output_dirs = ["wheelhouse"],
+)
+
+pip_library(
+    name = "fakepkg",
+    repo = ":wheelhouse",
+    version = "1.0.0",
+)
diff --git a/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/METADATA b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/METADATA
new file mode 100644
index 00000000..c2444db9
--- /dev/null
+++ b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/METADATA
@@ -0,0 +1,4 @@
+Metadata-Version: 2.4
+Name: fakepkg
+Version: 1.0.0
+License-Expression: MIT
diff --git a/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/RECORD b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/RECORD
new file mode 100644
index 00000000..c6a9efec
--- /dev/null
+++ b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/RECORD
@@ -0,0 +1,4 @@
+fakepkg/__init__.py,,
+fakepkg-1.0.0.dist-info/METADATA,,
+fakepkg-1.0.0.dist-info/WHEEL,,
+fakepkg-1.0.0.dist-info/RECORD,,
diff --git a/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/WHEEL b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/WHEEL
new file mode 100644
index 00000000..d3aa0df6
--- /dev/null
+++ b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg-1.0.0.dist-info/WHEEL
@@ -0,0 +1,4 @@
+Wheel-Version: 1.0
+Generator: fixture
+Root-Is-Purelib: true
+Tag: py3-none-any
diff --git a/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg/__init__.py b/test/license_expression_repo/third_party/python/fakepkg_src/fakepkg/__init__.py
new file mode 100644
index 00000000..e69de29b