diff --git a/src/createCustomer.c b/src/createCustomer.c
index d6226ee..e3a9920 100644
--- a/src/createCustomer.c
+++ b/src/createCustomer.c
@@ -31,10 +31,14 @@ void collectCustomerProperties()
 	}
 	if(inputTooLong){
 		errorMessage(-7);
-	}else{
+	}
+	else{
 	*(instance.forename+letterCounter) = '\0';
 	letterCounter = 0;
 	}
+	if(!isLetterOfAlphabet(instance.forename)){
+		errorMessage(-10);
+	}
 	printf("Enter surname (max. 15 letters):\n");
 	while(letterCounter<letterMaximum && (userInput=getchar())!='\n'){
 		*(instance.surname+letterCounter) = userInput;
@@ -50,6 +54,9 @@ void collectCustomerProperties()
 	*(instance.surname+letterCounter) = '\0';
 	letterCounter = 0;
 	}
+	if(!isLetterOfAlphabet(instance.surname)){
+		errorMessage(-11);
+	}
 	printf("Enter password (max. 20 letters):\n");
 	while(letterCounter<letterMaximum && (userInput=getchar())!='\n'){
 		*(instance.password+letterCounter) = userInput;
diff --git a/src/error.c b/src/error.c
index 137b60c..68294c1 100644
--- a/src/error.c
+++ b/src/error.c
@@ -45,6 +45,16 @@ int errorMessage(int errorCode)
 		returnValue = -9;
 		exit(-1);
 		break;
+	case -10:
+		puts("You have entered a digit for your forename. This is not allowed. Aborting!");
+		returnValue = -10;
+		exit(-1);
+		break;
+	case -11:
+		puts("You have entered a digit for your surname. This is not allowed. Aborting!");
+		returnValue = -11;
+		exit(-1);
+		break;
 	default:
 		puts("Error code unknown.");
 	}