Index: ext/fts5/fts5_expr.c
==================================================================
--- ext/fts5/fts5_expr.c
+++ ext/fts5/fts5_expr.c
@@ -1862,10 +1862,19 @@
   const char **azConfig;          /* Array of arguments for Fts5Config */
   const char *zNearsetCmd = "nearset";
   int nConfig;                    /* Size of azConfig[] */
   Fts5Config *pConfig = 0;
   int iArg = 1;
+
+  if( nArg<1 ){
+    char *zErr = sqlite3_mprintf("wrong number of arguments to function %s",
+        bTcl ? "fts5_expr_tcl" : "fts5_expr"
+    );
+    sqlite3_result_error(pCtx, zErr, -1);
+    sqlite3_free(zErr);
+    return;
+  }
 
   if( bTcl && nArg>1 ){
     zNearsetCmd = (const char*)sqlite3_value_text(apVal[1]);
     iArg = 2;
   }

Index: ext/fts5/test/fts5eb.test
==================================================================
--- ext/fts5/test/fts5eb.test
+++ ext/fts5/test/fts5eb.test
@@ -44,10 +44,17 @@
   12 {r+e OR w}                      {"r" + "e" OR "w"}
 } {
   do_execsql_test 1.$tn {SELECT fts5_expr($expr)} [list $res]
 }
 
+do_catchsql_test 2.1 {
+  SELECT fts5_expr()
+} {1 {wrong number of arguments to function fts5_expr}}
+
+do_catchsql_test 2.1 {
+  SELECT fts5_expr_tcl()
+} {1 {wrong number of arguments to function fts5_expr_tcl}}
 
 finish_test