diff --git a/src/eval.c b/src/eval.c
index dcaf2f0..c81ece1 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -5560,7 +5560,7 @@
 	    break;
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	    internal_error("tv_get_number(UNKNOWN)");
+	    internal_error_no_abort("tv_get_number(UNKNOWN)");
 	    break;
     }
     if (denote == NULL)		// useful for values that must be unsigned
@@ -5614,7 +5614,7 @@
 	    break;
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	    internal_error("tv_get_float(UNKNOWN)");
+	    internal_error_no_abort("tv_get_float(UNKNOWN)");
 	    break;
     }
     return 0;
@@ -5886,7 +5886,7 @@
 	    break;
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	    internal_error("copy_tv(UNKNOWN)");
+	    internal_error_no_abort("copy_tv(UNKNOWN)");
 	    break;
     }
 }
@@ -5965,7 +5965,7 @@
 	    break;
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	    internal_error("item_copy(UNKNOWN)");
+	    internal_error_no_abort("item_copy(UNKNOWN)");
 	    ret = FAIL;
     }
     --recurse;
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 3fce946..39e347a 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1890,10 +1890,7 @@
 #endif
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	    // Let's not use internal_error() here, otherwise
-	    // empty(test_unknown()) with ABORT_ON_INTERNAL_ERROR defined makes
-	    // Vim abort.
-	    semsg(_(e_intern2), "f_empty(UNKNOWN)");
+	    internal_error_no_abort("f_empty(UNKNOWN)");
 	    n = TRUE;
 	    break;
     }
@@ -8278,10 +8275,7 @@
 	case VAR_BLOB:    n = VAR_TYPE_BLOB; break;
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	     // Let's not use internal_error() here, otherwise
-	     // empty(test_unknown()) with ABORT_ON_INTERNAL_ERROR defined
-	     // makes Vim abort.
-	     semsg(_(e_intern2), "f_type(UNKNOWN)");
+	     internal_error_no_abort("f_type(UNKNOWN)");
 	     n = -1;
 	     break;
     }
diff --git a/src/json.c b/src/json.c
index d5e5782..f4a03e6 100644
--- a/src/json.c
+++ b/src/json.c
@@ -352,7 +352,7 @@
 #endif
 	case VAR_UNKNOWN:
 	case VAR_VOID:
-	    internal_error("json_encode_item()");
+	    internal_error_no_abort("json_encode_item()");
 	    return FAIL;
     }
     return OK;
diff --git a/src/message.c b/src/message.c
index c2855fb..cb1a773 100644
--- a/src/message.c
+++ b/src/message.c
@@ -838,6 +838,16 @@
     siemsg(_(e_intern2), where);
 }
 
+/*
+ * Like internal_error() but do not call abort(), to avoid tests using
+ * test_unknown() and test_void() causing Vim to exit.
+ */
+    void
+internal_error_no_abort(char *where)
+{
+     semsg(_(e_intern2), where);
+}
+
 // emsg3() and emsgn() are in misc2.c to avoid warnings for the prototypes.
 
     void
diff --git a/src/proto/message.pro b/src/proto/message.pro
index 5c9ca6c..16c3354 100644
--- a/src/proto/message.pro
+++ b/src/proto/message.pro
@@ -12,6 +12,7 @@
 int emsg(char *s);
 void iemsg(char *s);
 void internal_error(char *where);
+void internal_error_no_abort(char *where);
 void emsg_invreg(int name);
 void emsg_namelen(char *msg, char_u *name, int len);
 char *msg_trunc_attr(char *s, int force, int attr);
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 6f3b81a..ef4180a 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -63,6 +63,16 @@
   call assert_fails("call empty(test_unknown())", 'E685:')
 endfunc
 
+func Test_test_void()
+  call assert_fails('echo 1 == test_void()', 'E685:')
+  if has('float')
+    call assert_fails('echo 1.0 == test_void()', 'E685:')
+  endif
+  call assert_fails('let x = json_encode(test_void())', 'E685:')
+  call assert_fails('let x = copy(test_void())', 'E685:')
+  call assert_fails('let x = copy([test_void()])', 'E685:')
+endfunc
+
 func Test_len()
   call assert_equal(1, len(0))
   call assert_equal(2, len(12))
diff --git a/src/version.c b/src/version.c
index a828963..4dc9642 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    334,
+/**/
     333,
 /**/
     332,