diff --git a/eval/eval.go b/eval/eval.go
index 34fc504..6948df9 100644
--- a/eval/eval.go
+++ b/eval/eval.go
@@ -344,7 +344,14 @@ func (ev *Eval) eval(exp primitive.Primitive, e *env.Environment, expandMacro bo
 		//
 		// Now we're only dealing with lists
 		//
-		listExp := exp.(primitive.List)
+		listExp, listOk := exp.(primitive.List)
+
+		//
+		// But just in case we're not ..
+		//
+		if !listOk {
+			return primitive.Error(fmt.Sprintf("argument not a list for a function call: %v", exp))
+		}
 
 		//
 		// Is this an empty list?  Then just return it
diff --git a/eval/eval_test.go b/eval/eval_test.go
index ae056ba..c13475d 100644
--- a/eval/eval_test.go
+++ b/eval/eval_test.go
@@ -390,6 +390,10 @@ a
 		{input: "(define blah (lambda (a:number) (print a))) (blah '(3))", output: "ERROR{TypeError - argument a to blah was supposed to be number, got list}"},
 		{input: "(define blah (lambda (a:function) (print a))) (blah '(3))", output: "ERROR{TypeError - argument a to blah was supposed to be function, got list}"},
 		{input: "(define blah (lambda (a:any) (print a))) (blah '(3))", output: "(3)"},
+
+		// fuzz errors
+		{input: "(defmacro! unless(fn*()`(~!)))(unless )", output: "ERROR{argument '(lambda (x) (if x #f #t))' not a function}"},
+		{input: "(ord 0)", output: "ERROR{argument not a character/string, got number}"},
 	}
 
 	for _, test := range tests {
diff --git a/fuzz_test.go b/fuzz_test.go
index b90be2d..a3e4f15 100644
--- a/fuzz_test.go
+++ b/fuzz_test.go
@@ -126,6 +126,7 @@ func FuzzYAL(f *testing.F) {
 		"invalid character literal",
 		"is not a symbol",
 		"must have even length",
+		"not a character",
 		"not a function",
 		"not a hash",
 		"not a list",
diff --git a/testdata/fuzz/FuzzYAL/ba0fcef6ab521763179f52a1f2ef9fed78574074e826d61f9c362bd4ca07f62e b/testdata/fuzz/FuzzYAL/ba0fcef6ab521763179f52a1f2ef9fed78574074e826d61f9c362bd4ca07f62e
new file mode 100644
index 0000000..8c7e9f4
--- /dev/null
+++ b/testdata/fuzz/FuzzYAL/ba0fcef6ab521763179f52a1f2ef9fed78574074e826d61f9c362bd4ca07f62e
@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("(defmacro! unless(fn*()`(~!)))(unless )")