diff -r cf57e8c78492 -r 86d8bbc99e7b src/AwkHandler.h
--- a/src/AwkHandler.h	Thu May 23 23:35:52 2019 +0200
+++ b/src/AwkHandler.h	Sat May 25 11:36:31 2019 +0200
@@ -133,9 +133,11 @@
 	void cleanUp() {
 		if (awkInputWriterFD >= 0) {
 			closeOrThrow(awkInputWriterFD);
-			// FIXME: check exit codes
-			__pid_t waitResult1 = wait(NULL);
-			__pid_t waitResult2 = wait(NULL);
+			int error1;
+			int error2;
+			__pid_t waitPID1 = wait(&error1);
+			__pid_t waitPID2 = wait(&error2);
+			if (error1 || error2) throw cli::RelpipeCLIException(L"The child process returned an error exit code.", cli::CLI::EXIT_CODE_UNEXPECTED_ERROR); // TODO: better exceptions?
 			awkInputWriterFD = -1;
 		}