diff --git a/src/cmd/5a/lex.c b/src/cmd/5a/lex.c
index 3ce1bfe9524..d997754fd3a 100644
--- a/src/cmd/5a/lex.c
+++ b/src/cmd/5a/lex.c
@@ -68,7 +68,7 @@ main(int argc, char *argv[])
 	ARGBEGIN {
 	default:
 		c = ARGC();
-		if(c >= 0 || c < sizeof(debug))
+		if(c >= 0 && c < sizeof(debug))
 			debug[c] = 1;
 		break;
 
diff --git a/src/cmd/6a/lex.c b/src/cmd/6a/lex.c
index 89143e78941..290785c551d 100644
--- a/src/cmd/6a/lex.c
+++ b/src/cmd/6a/lex.c
@@ -74,7 +74,7 @@ main(int argc, char *argv[])
 	ARGBEGIN {
 	default:
 		c = ARGC();
-		if(c >= 0 || c < sizeof(debug))
+		if(c >= 0 && c < sizeof(debug))
 			debug[c] = 1;
 		break;
 
diff --git a/src/cmd/8a/lex.c b/src/cmd/8a/lex.c
index a7840f6258a..2e690851293 100644
--- a/src/cmd/8a/lex.c
+++ b/src/cmd/8a/lex.c
@@ -74,7 +74,7 @@ main(int argc, char *argv[])
 	ARGBEGIN {
 	default:
 		c = ARGC();
-		if(c >= 0 || c < sizeof(debug))
+		if(c >= 0 && c < sizeof(debug))
 			debug[c] = 1;
 		break;