diff --git a/toolchain/diagnostics/check_diagnostics.py b/toolchain/diagnostics/check_diagnostics.py
index c4e74db735b9..baaa9082e5ad 100755
--- a/toolchain/diagnostics/check_diagnostics.py
+++ b/toolchain/diagnostics/check_diagnostics.py
@@ -56,7 +56,9 @@ def load_diagnostic_kind() -> Set[str]:
     """
     path = Path("toolchain/diagnostics/kind.def")
     content = path.read_text()
-    decls = set(re.findall(r"^\s+CARBON_DIAGNOSTIC_KIND\((.+)\)", content))
+    decls = set(
+        re.findall(r"^CARBON_DIAGNOSTIC_KIND\((.+)\)", content, flags=re.M)
+    )
     return decls.difference(IGNORED)
 
 
@@ -71,9 +73,13 @@ def load_diagnostic_uses_in(
     line_offset = 0
 
     found: Dict[str, List[Loc]] = collections.defaultdict(lambda: [])
-    for m in re.finditer(r"CARBON_DIAGNOSTIC\(\s*(\w+),", content):
+    # `CARBON_DIAGNOSTIC_ON_SCOPE` declares a diagnostic too; the definitions of
+    # both macros name their own parameter, which is not a use.
+    for m in re.finditer(
+        r"(?<!#define )CARBON_DIAGNOSTIC(?:_ON_SCOPE)?\(\s*(\w+),", content
+    ):
         diag = m.group(1)
-        if diag in IGNORED:
+        if diag in IGNORED or diag in ("DiagnosticName",):
             continue
         line += content.count("\n", line_offset, m.start())
         line_offset = m.start()
diff --git a/toolchain/diagnostics/coverage_test.cpp b/toolchain/diagnostics/coverage_test.cpp
index 3409283916e2..e3368f879e70 100644
--- a/toolchain/diagnostics/coverage_test.cpp
+++ b/toolchain/diagnostics/coverage_test.cpp
@@ -31,9 +31,6 @@ constexpr Kind UntestedKinds[] = {
 
     // Diagnosing erroneous install conditions, but test environments are
     // typically correct.
-    Kind::BuildFailureRunningClangToLink,
-    Kind::BuildOutputFileOpenError,
-    Kind::BuildPreludeManifestError,
     Kind::BuildTempDirectoryCreationError,
     Kind::BuildTempDirectoryDeletionError,
     Kind::CompileCoreManifestError,
diff --git a/toolchain/diagnostics/kind.def b/toolchain/diagnostics/kind.def
index 11d2704c891c..7b640c503616 100644
--- a/toolchain/diagnostics/kind.def
+++ b/toolchain/diagnostics/kind.def
@@ -25,9 +25,6 @@ CARBON_DIAGNOSTIC_KIND(DriverInstallInvalid)
 CARBON_DIAGNOSTIC_KIND(DriverRuntimesCacheInvalid)
 CARBON_DIAGNOSTIC_KIND(DriverPrebuiltRuntimesInvalid)
 CARBON_DIAGNOSTIC_KIND(DriverCommandLineParseFailed)
-CARBON_DIAGNOSTIC_KIND(BuildFailureRunningClangToLink)
-CARBON_DIAGNOSTIC_KIND(BuildOutputFileOpenError)
-CARBON_DIAGNOSTIC_KIND(BuildPreludeManifestError)
 CARBON_DIAGNOSTIC_KIND(BuildTempDirectoryCreationError)
 CARBON_DIAGNOSTIC_KIND(BuildTempDirectoryDeletionError)
 CARBON_DIAGNOSTIC_KIND(CompileCoreManifestError)