diff --git a/HISTORY b/HISTORY
index 29bf732..61f86e5 100755
--- a/HISTORY
+++ b/HISTORY
@@ -1,3 +1,6 @@
+Apr. 26 2016
+Added an invalid operation usage error when met unexpected expression
+
 Apr. 22 2016
 Added UTF8 token support
 
diff --git a/core/my_basic.c b/core/my_basic.c
index abff666..00ae53a 100755
--- a/core/my_basic.c
+++ b/core/my_basic.c
@@ -228,6 +228,7 @@ static const char* _ERR_DESC[] = {
 	"Illegal bound",
 	"Too much dimensions",
 	"Operation failed",
+	"Invalid operation usage",
 	"Dimension count out of bound",
 	"Out of bound",
 	"Label does not exist",
@@ -3657,6 +3658,10 @@ _var:
 				if(_IS_FUNC(c, _core_close_bracket))
 					hack = true;
 
+				break;
+			case ' ':
+				_handle_error_on_obj(s, SE_RN_INVALID_OPERATION_USAGE, s->source_file, errn ? DON(errn) : DON(ast), MB_FUNC_ERR, _error, result);
+
 				break;
 			}
 		}
diff --git a/core/my_basic.h b/core/my_basic.h
index f1cdf99..4965db8 100755
--- a/core/my_basic.h
+++ b/core/my_basic.h
@@ -361,6 +361,7 @@ typedef enum mb_error_e {
 	SE_RN_ILLEGAL_BOUND,
 	SE_RN_TOO_MUCH_DIMENSIONS,
 	SE_RN_OPERATION_FAILED,
+	SE_RN_INVALID_OPERATION_USAGE,
 	SE_RN_DIMENSION_COUNT_OUT_OF_BOUND,
 	SE_RN_ARRAY_OUT_OF_BOUND,
 	SE_RN_LABEL_NOT_EXISTS,
diff --git a/output/my_basic.exe b/output/my_basic.exe
index 26f84d8..30f65e5 100755
Binary files a/output/my_basic.exe and b/output/my_basic.exe differ