diff --git a/rules/scala.bzl b/rules/scala.bzl
index d91c77062..bebb524c1 100644
--- a/rules/scala.bzl
+++ b/rules/scala.bzl
@@ -87,6 +87,7 @@ _compile_attributes = {
             "-src.jar",
         ],
         flags = ["DIRECT_COMPILE_TIME_INPUT"],
+        mandatory = True,
     ),
     "data": attr.label_list(
         cfg = _scala_outgoing_transition,
diff --git a/src/main/scala/BUILD b/src/main/scala/BUILD
index 2b72858e7..965b541c4 100644
--- a/src/main/scala/BUILD
+++ b/src/main/scala/BUILD
@@ -51,6 +51,7 @@ register_zinc_toolchain(
 # IntelliJ libraries, so we can get a Scala SDK on sync.
 scala_library(
     name = "scala-sdk",
+    srcs = [],
     deps_used_whitelist = compiler_classpath_2_13,
     scala_toolchain_name = "annex_zinc_3",
     deps = compiler_classpath_2_13,
@@ -69,6 +70,7 @@ runtime_classpath_3 = [
 
 scala_library(
     name = "scala-sdk-3",
+    srcs = [],
     deps_used_whitelist = compiler_classpath_3,
     scala_toolchain_name = "annex_zinc_3",
     deps = compiler_classpath_3,
diff --git a/tests/binary/resource/BUILD b/tests/binary/resource/BUILD
index bc083100c..975f10c25 100644
--- a/tests/binary/resource/BUILD
+++ b/tests/binary/resource/BUILD
@@ -9,6 +9,7 @@ scala_library(
 
 scala_binary(
     name = "bin",
+    srcs = [],
     main_class = "Example",
     resource_strip_prefix = package_name(),
     resources = ["example.txt"],
diff --git a/tests/dependencies/validation_action/BUILD.bazel b/tests/dependencies/validation_action/BUILD.bazel
index c661ba9e5..bf8cb7745 100644
--- a/tests/dependencies/validation_action/BUILD.bazel
+++ b/tests/dependencies/validation_action/BUILD.bazel
@@ -2,6 +2,7 @@ load("@rules_scala_annex//rules:scala.bzl", "scala_library")
 
 scala_library(
     name = "validation_action",
+    srcs = [],
     scala_toolchain_name = "test_zinc_2_13",
     tags = ["manual"],
 )
diff --git a/tests/plugins/semanticdb/BUILD b/tests/plugins/semanticdb/BUILD
index b5362b6b7..e2d9b55c3 100644
--- a/tests/plugins/semanticdb/BUILD
+++ b/tests/plugins/semanticdb/BUILD
@@ -60,6 +60,7 @@ read_semanticdb_info(
 
 scala_library(
     name = "semanticdb-empty",
+    srcs = [],
     scala_toolchain_name = "scala_2_13_with_semanticdb",
 )
 
diff --git a/tests/resources/maven/BUILD b/tests/resources/maven/BUILD
index e83914382..f597a9634 100644
--- a/tests/resources/maven/BUILD
+++ b/tests/resources/maven/BUILD
@@ -2,6 +2,7 @@ load("@rules_scala_annex//rules:scala.bzl", "scala_library")
 
 scala_library(
     name = "maven",
+    srcs = [],
     resources = glob(["src/main/resources/*"]),
     scala_toolchain_name = "test_zinc_2_13",
 )
diff --git a/tests/resources/plain/BUILD b/tests/resources/plain/BUILD
index aa5349e5b..b9fc09464 100644
--- a/tests/resources/plain/BUILD
+++ b/tests/resources/plain/BUILD
@@ -2,12 +2,14 @@ load("@rules_scala_annex//rules:scala.bzl", "scala_library")
 
 scala_library(
     name = "plain",
+    srcs = [],
     resources = glob(["**/*.txt"]),
     scala_toolchain_name = "test_zinc_2_13",
 )
 
 scala_library(
     name = "merged",
+    srcs = [],
     resource_jars = [":plain"],
     resource_strip_prefix = "resources",
     resources = glob(["**/*.txt"]),
diff --git a/tests/resources/prefix/BUILD b/tests/resources/prefix/BUILD
index ebe7a5f4a..88e183616 100644
--- a/tests/resources/prefix/BUILD
+++ b/tests/resources/prefix/BUILD
@@ -2,6 +2,7 @@ load("@rules_scala_annex//rules:scala.bzl", "scala_library")
 
 scala_library(
     name = "prefix",
+    srcs = [],
     resource_strip_prefix = package_name(),
     resources = glob(["**/*.txt"]),
     scala_toolchain_name = "test_zinc_2_13",
@@ -9,6 +10,7 @@ scala_library(
 
 scala_library(
     name = "outside",
+    srcs = [],
     resource_strip_prefix = "{}/other".format(package_name()),
     resources = glob(["**/*.txt"]),
     scala_toolchain_name = "test_zinc_2_13",
diff --git a/tests/resources/reference_conf/BUILD b/tests/resources/reference_conf/BUILD
index 6333322b7..90e70cb75 100644
--- a/tests/resources/reference_conf/BUILD
+++ b/tests/resources/reference_conf/BUILD
@@ -3,6 +3,7 @@ load("@rules_scala_annex//rules:scala.bzl", "scala_library")
 
 scala_library(
     name = "plain",
+    srcs = [],
     resource_strip_prefix = "resources/reference_conf",
     resources = ["reference.conf"],
     scala_toolchain_name = "test_zinc_2_13",
diff --git a/tests/resources/special_characters/BUILD b/tests/resources/special_characters/BUILD
index 9b980cd1d..45f435876 100644
--- a/tests/resources/special_characters/BUILD
+++ b/tests/resources/special_characters/BUILD
@@ -2,6 +2,7 @@ load("@rules_scala_annex//rules:scala.bzl", "scala_library")
 
 scala_library(
     name = "special_characters",
+    srcs = [],
     resources = glob(["**/*.txt"]),
     scala_toolchain_name = "test_zinc_2_13",
 )