diff --git a/src/exec.c b/src/exec.c
index a28a8e3..7457ef1 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -32,6 +32,11 @@ ASTNumData exec_call(AST* ast) {
         ASTNumData n2 = exec_expr(calldata->argv[1]);
 
         return n1 + n2;
+    } else if (!strcmp(calldata->to, "-") && calldata->argc == 2) {
+        ASTNumData n1 = exec_expr(calldata->argv[0]);
+        ASTNumData n2 = exec_expr(calldata->argv[1]);
+
+        return n1 - n2;
     }
     return -1000;
 }
diff --git a/src/grammar.y b/src/grammar.y
index 32dd406..862a6d9 100644
--- a/src/grammar.y
+++ b/src/grammar.y
@@ -22,6 +22,7 @@
 %define parse.error verbose
 
 %token<fval> NUM
+%token NEG
 %token<strval> CALL
 %token PLUS
 %token NL
@@ -36,11 +37,30 @@ input:
 
 exp:
     NUM { $$ = ast_init(AST_TYPE_NUM, ast_num_data_init($1)); }
+    | NEG NUM { $$ = ast_init(AST_TYPE_NUM, ast_num_data_init(-$2)); }
     | NUM PLUS NUM {
         AST** argv = calloc(2, sizeof(AST*));
         argv[0] = ast_init(AST_TYPE_NUM, ast_num_data_init($1));
         argv[1] = ast_init(AST_TYPE_NUM, ast_num_data_init($3));
         $$ = ast_init(AST_TYPE_CALL, ast_call_data_init("+", 2, argv));
     }
+    | NEG NUM PLUS NUM {
+        AST** argv = calloc(2, sizeof(AST*));
+        argv[0] = ast_init(AST_TYPE_NUM, ast_num_data_init(-$2));
+        argv[1] = ast_init(AST_TYPE_NUM, ast_num_data_init($4));
+        $$ = ast_init(AST_TYPE_CALL, ast_call_data_init("+", 2, argv));
+    }
+    | NUM NEG NUM {
+        AST** argv = calloc(2, sizeof(AST*));
+        argv[0] = ast_init(AST_TYPE_NUM, ast_num_data_init($1));
+        argv[1] = ast_init(AST_TYPE_NUM, ast_num_data_init($3));
+        $$ = ast_init(AST_TYPE_CALL, ast_call_data_init("-", 2, argv));
+    }
+    | NEG NUM NEG NUM {
+        AST** argv = calloc(2, sizeof(AST*));
+        argv[0] = ast_init(AST_TYPE_NUM, ast_num_data_init(-$2));
+        argv[1] = ast_init(AST_TYPE_NUM, ast_num_data_init($4));
+        $$ = ast_init(AST_TYPE_CALL, ast_call_data_init("-", 2, argv));
+    }
 
 %%
diff --git a/src/lexer.c b/src/lexer.c
index 73ead29..9313c75 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -65,6 +65,7 @@ int yylex() {
     switch (c) {
         case '+':  return PLUS;
         case '\n': return NL;
+        case '-':  return NEG;
         default:   return CALL;
     }