diff --git a/dtc-lexer.l b/dtc-lexer.l
index 0ee1caf..22dda7d 100644
--- a/dtc-lexer.l
+++ b/dtc-lexer.l
@@ -153,7 +153,10 @@ static void lexical_error(const char *fmt, ...);
 			errno = 0;
 			yylval.integer = strtoull(yytext, &e, 0);
 
-			assert(!(*e) || !e[strspn(e, "UL")]);
+			if (*e && e[strspn(e, "UL")]) {
+				lexical_error("Bad integer literal '%s'",
+					      yytext);
+			}
 
 			if (errno == ERANGE)
 				lexical_error("Integer literal '%s' out of range",
diff --git a/tests/bad-octal-literal.dts b/tests/bad-octal-literal.dts
new file mode 100644
index 0000000..26558a2
--- /dev/null
+++ b/tests/bad-octal-literal.dts
@@ -0,0 +1,5 @@
+/dts-v1/;
+
+/ {
+	x = <09>;
+};
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index 3d6a230..7bdf8e0 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -291,6 +291,7 @@ libfdt_tests () {
     run_dtc_test -I dts -O dtb bad-size-cells.dts
 
     run_wrap_error_test $DTC division-by-zero.dts
+    run_wrap_error_test $DTC bad-octal-literal.dts
 }
 
 dtc_tests () {