diff --git a/fuzzer_runner/pyproject.toml b/fuzzer_runner/pyproject.toml
index e1a80aaa..242af9f1 100644
--- a/fuzzer_runner/pyproject.toml
+++ b/fuzzer_runner/pyproject.toml
@@ -25,6 +25,11 @@ packages = ["src/buttercup"]
 requires = ["hatchling"]
 build-backend = "hatchling.build"
 
+[tool.uv]
+# Must match OSS-Fuzz protobuf version for compatibility
+# See: https://github.com/google/oss-fuzz/blob/master/infra/base-images/base-builder/Dockerfile
+constraint-dependencies = ["protobuf==3.20.3"]
+
 [tool.uv.sources]
 common = { path = "../common", editable = true }
 
diff --git a/fuzzer_runner/uv.lock b/fuzzer_runner/uv.lock
index 8e724d23..645c698f 100644
--- a/fuzzer_runner/uv.lock
+++ b/fuzzer_runner/uv.lock
@@ -2,6 +2,9 @@ version = 1
 revision = 3
 requires-python = "==3.12.*"
 
+[manifest]
+constraints = [{ name = "protobuf", specifier = "==3.20.3" }]
+
 [[package]]
 name = "annotated-types"
 version = "0.7.0"