diff --git a/README.md b/README.md
index a33e3d9..161052a 100644
--- a/README.md
+++ b/README.md
@@ -65,16 +65,16 @@ mumble> eval { head {1 2 3} }
 mumble> (eval { head {+ tail head } } ) 1 2 3 
 mumble> len {1 2 3}
 mumble> join { {1 2} {3 4} }
-mumble> def {x} { 100 }
+mumble> def { {x} { 100 } }
 mumble> x
-mumble> def { a b c } { 1 2 3}
+mumble> def { { a b c } { 1 2 3} }
 mumble> * a b c
 mumble> - a b c
 mumble> / a b c
 mumble> VERBOSITY=0
 mumble> VERBOSITY=1
 mumble> VERBOSITY=2
-mumble> def {plus} {(@ {x y} {+ x y})}
+mumble> def { {plus} {(@ {x y} {+ x y})} }
 ( )
 mumble> plus
 ( @ { x y } { + x y } )
diff --git a/mumble b/mumble
index 2fbef48..dbb2d8d 100755
Binary files a/mumble and b/mumble differ
diff --git a/src/mumble.c b/src/mumble.c
index 650104d..224146b 100644
--- a/src/mumble.c
+++ b/src/mumble.c
@@ -733,20 +733,19 @@ lispval* builtin_join(lispval* l, lispenv* e)
 // Define a variable
 lispval* builtin_def(lispval* v, lispenv* env)
 {
-    // Takes two arguments: def { a b } { 1 2 }
-    LISPVAL_ASSERT(v->count == 2, "Error: function def passed something other than 2 arguments");
-		
-		lispval* symbols = v->cell[0];
-		lispval* values = v->cell[1];
-		symbols = evaluate_lispval(symbols, env);
-		values = evaluate_lispval(values, env);
-    
-		LISPVAL_ASSERT(symbols->type == LISPVAL_QEXPR, "Error: Argument passed to def is not a q-expr, i.e., a bracketed list.");
-		LISPVAL_ASSERT(values->type == LISPVAL_QEXPR, "Error: Argument passed to def is not a q-expr, i.e., a bracketed list.");
-    LISPVAL_ASSERT(symbols->count == values->count, "Error: In function \"def\" both subarguments should have the same length");
+    // Takes one argument: def { { a b } { 1 2 } }
+    lispval* source = v->cell[0];
+    LISPVAL_ASSERT(v->count == 1, "Error: function def passed too many arguments");
+    LISPVAL_ASSERT(source->type == LISPVAL_QEXPR, "Error: Argument passed to def is not a q-expr, i.e., a bracketed list.");
+    LISPVAL_ASSERT(source->count == 2, "Error: Argument passed to def should be a q expr with two q expressions as children: def { { a b } { 1 2 } } ");
+    LISPVAL_ASSERT(source->cell[0]->type == LISPVAL_QEXPR, "Error: Argument passed to def should be a q expr with two q expressions as children: def { { a b } { 1 2 } } ");
+    LISPVAL_ASSERT(source->cell[1]->type == LISPVAL_QEXPR || source->cell[1]->type == LISPVAL_SEXPR, "Error: Argument passed to def should be a q expr with two q expressions as children: def { { a b } { 1 2 } } ");
+    LISPVAL_ASSERT(source->cell[0]->count == source->cell[1]->count, "Error: In function \"def\" both subarguments should have the same length");
 
+    lispval* symbols = source->cell[0];
+    lispval* values = source->cell[1];
     for (int i = 0; i < symbols->count; i++) {
-        LISPVAL_ASSERT(symbols->cell[i]->type == LISPVAL_SYM, "Error: in function def, the first list of items should be of type symbol:  def { a b } { 1 2 } ");
+        LISPVAL_ASSERT(symbols->cell[i]->type == LISPVAL_SYM, "Error: in function def, the first list of items should be of type symbol:  def { { a b } { 1 2 } }");
         if (VERBOSE)
             print_lispval_tree(symbols, 0);
         if (VERBOSE)