diff --git a/src/asm/lexer.c b/src/asm/lexer.c
index a98fef81..e47032d3 100644
--- a/src/asm/lexer.c
+++ b/src/asm/lexer.c
@@ -471,17 +471,17 @@ void yylex_GetFloatMaskAndFloatLen(uint32_t *pnFloatMask, uint32_t *pnFloatLen)
 
 	char *s = pLexBuffer;
 	uint32_t nOldFloatMask = 0;
-	uint32_t nFloatMask = tFloatingFirstChar[(int32_t)*s];
+	uint32_t nFloatMask = tFloatingFirstChar[(uint8_t)*s];
 
 	if (nFloatMask != 0) {
 		s++;
 		nOldFloatMask = nFloatMask;
-		nFloatMask &= tFloatingSecondChar[(int32_t)*s];
+		nFloatMask &= tFloatingSecondChar[(uint8_t)*s];
 
 		while (nFloatMask != 0) {
 			s++;
 			nOldFloatMask = nFloatMask;
-			nFloatMask &= tFloatingChars[(int32_t)*s];
+			nFloatMask &= tFloatingChars[(uint8_t)*s];
 		}
 	}
 
diff --git a/test/asm/garbage_char.asm b/test/asm/garbage_char.asm
new file mode 100644
index 00000000..ca5f132c
--- /dev/null
+++ b/test/asm/garbage_char.asm
@@ -0,0 +1 @@
+xÿ
\ No newline at end of file
diff --git a/test/asm/garbage_char.out b/test/asm/garbage_char.out
new file mode 100644
index 00000000..a05e4960
--- /dev/null
+++ b/test/asm/garbage_char.out
@@ -0,0 +1,3 @@
+ERROR: garbage_char.asm(1):
+    syntax error
+error: Assembly aborted (1 errors)!
diff --git a/test/asm/garbage_char.out.pipe b/test/asm/garbage_char.out.pipe
new file mode 100644
index 00000000..1ba12ddc
--- /dev/null
+++ b/test/asm/garbage_char.out.pipe
@@ -0,0 +1,3 @@
+ERROR: -(1):
+    syntax error
+error: Assembly aborted (1 errors)!