diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index a5dbb5a37be..853609da31e 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -2332,7 +2332,7 @@ namespace ts {
 
         function parseProjectReferenceConfigFile(ref: ProjectReference): { commandLine: ParsedCommandLine, sourceFile: SourceFile } | undefined {
             // The actual filename (i.e. add "/tsconfig.json" if necessary)
-            const refPath = resolveProjectReferencePath(host, ref)!; // TODO: GH#18217
+            const refPath = resolveProjectReferencePath(host, ref);
             // An absolute path pointing to the containing directory of the config file
             const basePath = getNormalizedAbsolutePath(getDirectoryPath(refPath), host.getCurrentDirectory());
             const sourceFile = host.getSourceFile(refPath, ScriptTarget.JSON) as JsonSourceFile;
diff --git a/src/compiler/tsbuild.ts b/src/compiler/tsbuild.ts
index 57af6a18ada..9055fc1030c 100644
--- a/src/compiler/tsbuild.ts
+++ b/src/compiler/tsbuild.ts
@@ -1111,7 +1111,7 @@ namespace ts {
                     newestDeclarationFileContentChangedTime = newer(unchangedTime, newestDeclarationFileContentChangedTime);
                 }
                 else {
-                    newestDeclarationFileContentChangedTime = newer(newestDeclarationFileContentChangedTime, host.getModifiedTime!(output));
+                    newestDeclarationFileContentChangedTime = newer(newestDeclarationFileContentChangedTime, host.getModifiedTime(output));
                 }
             }
         }