diff --git a/msh.c b/msh.c
index 590a655..fe66427 100644
--- a/msh.c
+++ b/msh.c
@@ -318,7 +318,9 @@ int mathTest() {
 		#endif
 		printf("%d %c %d = ", num1, mathOperation[randProblem], num2);
 		numLine = readline("");
-		sscanf(numLine, "%ld", &numAnswer);
+		if (numLine != NULL && strlen(numLine) > 0) {
+		  sscanf(numLine, "%ld", &numAnswer);
+		}
 
 		if (numSolution != numAnswer) { // If wrong answer
 			status = 1;