diff --git a/src/sentry/api/endpoints/source_map_debug.py b/src/sentry/api/endpoints/source_map_debug.py
index ca012244cca0..7a649eeebb5e 100644
--- a/src/sentry/api/endpoints/source_map_debug.py
+++ b/src/sentry/api/endpoints/source_map_debug.py
@@ -44,6 +44,13 @@
 from sentry.utils import json, metrics
 from sentry.utils.javascript import find_sourcemap
 from sentry.utils.safe import get_path
+
+
+def _sourcemap_header(headers: Mapping[str, object]) -> str | None:
+    value = headers.get("sourcemap", headers.get("x-sourcemap"))
+    return value if isinstance(value, str) else None
+
+
 from sentry.utils.urls import non_standard_url_join
 
 logger = logging.getLogger(__name__)
@@ -431,18 +438,18 @@ def _find_source_file_in_basic_uploaded_files(self) -> None:
             ):
                 self.source_file_lookup_result = "found"
                 self.found_source_file_name = possible_release_file.name
-                sourcemap_header = None
+                sourcemap_bytes: bytes | None = None
                 if possible_release_file.file.headers:
                     headers = ArtifactBundleArchive.normalize_headers(
                         possible_release_file.file.headers
                     )
-                    sourcemap_header = headers.get("sourcemap", headers.get("x-sourcemap"))
-                    sourcemap_header = (
+                    sourcemap_header = _sourcemap_header(headers)
+                    sourcemap_bytes = (
                         force_bytes(sourcemap_header) if sourcemap_header is not None else None
                     )
                 try:
                     source_map_reference = find_sourcemap(
-                        sourcemap_header, possible_release_file.file.getfile().read()
+                        sourcemap_bytes, possible_release_file.file.getfile().read()
                     )
                     self.source_map_reference = (
                         force_str(source_map_reference)
@@ -482,14 +489,14 @@ def _find_source_file_in_artifact_indexes(self) -> None:
                                 self.found_source_file_name
                             )
                             headers = ArtifactBundleArchive.normalize_headers(headers)
-                            sourcemap_header = headers.get("sourcemap", headers.get("x-sourcemap"))
-                            sourcemap_header = (
+                            sourcemap_header = _sourcemap_header(headers)
+                            sourcemap_bytes = (
                                 force_bytes(sourcemap_header)
                                 if sourcemap_header is not None
                                 else None
                             )
                             source_map_reference = find_sourcemap(
-                                sourcemap_header, source_file.read()
+                                sourcemap_bytes, source_file.read()
                             )
                             self.source_map_reference = (
                                 force_str(source_map_reference)
@@ -529,15 +536,15 @@ def _find_source_file_in_artifact_bundles(self) -> None:
                             headers = ArtifactBundleArchive.normalize_headers(headers)
                             self.source_file_lookup_result = "found"
                             self.found_source_file_name = potential_source_file_name
-                            sourcemap_header = headers.get("sourcemap", headers.get("x-sourcemap"))
-                            sourcemap_header = (
+                            sourcemap_header = _sourcemap_header(headers)
+                            sourcemap_bytes = (
                                 force_bytes(sourcemap_header)
                                 if sourcemap_header is not None
                                 else None
                             )
                             try:
                                 source_map_reference = find_sourcemap(
-                                    sourcemap_header, matching_file.read()
+                                    sourcemap_bytes, matching_file.read()
                                 )
                                 self.source_map_reference = (
                                     force_str(source_map_reference)
diff --git a/tests/sentry/api/endpoints/test_source_map_debug.py b/tests/sentry/api/endpoints/test_source_map_debug.py
index 443ccbf55555..4230b0b81d2f 100644
--- a/tests/sentry/api/endpoints/test_source_map_debug.py
+++ b/tests/sentry/api/endpoints/test_source_map_debug.py
@@ -15,6 +15,7 @@
     MIN_JS_SDK_VERSION_FOR_DEBUG_IDS,
     ReleaseBundleUrls,
     SourceMapReleaseProcessResult,
+    _sourcemap_header,
     get_release_bundle_urls,
     report_unsuccessful_url_matches,
 )
@@ -34,6 +35,13 @@
 from sentry.testutils.helpers.options import override_options
 from sentry.testutils.skips import requires_snuba
 
+
+def test_sourcemap_header_ignores_non_strings() -> None:
+    assert _sourcemap_header({"sourcemap": "foo"}) == "foo"
+    assert _sourcemap_header({"x-sourcemap": "bar"}) == "bar"
+    assert _sourcemap_header({"sourcemap": 1}) is None
+
+
 pytestmark = [requires_snuba]