diff --git a/expand/expand.go b/expand/expand.go
index 3c4343da..5e52ae05 100644
--- a/expand/expand.go
+++ b/expand/expand.go
@@ -214,6 +214,9 @@ const patMode = pattern.Filenames | pattern.Braces
 // The config specifies shell expansion options; nil behaves the same as an
 // empty config.
 func Pattern(cfg *Config, word *syntax.Word) (string, error) {
+	if word == nil {
+		return "", nil
+	}
 	cfg = prepareConfig(cfg)
 	field, err := cfg.wordField(word.Parts, quoteNone)
 	if err != nil {
diff --git a/expand/param.go b/expand/param.go
index f876ef0b..07d3e13b 100644
--- a/expand/param.go
+++ b/expand/param.go
@@ -206,6 +206,9 @@ func (cfg *Config) paramExp(pe *syntax.ParamExp) (string, error) {
 		if err != nil {
 			return "", err
 		}
+		if orig == "" {
+			break // nothing to replace
+		}
 		with, err := Literal(cfg, pe.Repl.With)
 		if err != nil {
 			return "", err
diff --git a/interp/interp_test.go b/interp/interp_test.go
index d2312412..11ab2873 100644
--- a/interp/interp_test.go
+++ b/interp/interp_test.go
@@ -509,6 +509,7 @@ var runTests = []runTest{
 	{"a='abcx1y'; echo ${a//x[[:digit:]]y}", "abc\n"},
 	{`a=xyz; echo "${a/y/a  b}"`, "xa  bz\n"},
 	{"a='foo_interp_missing/bar_interp_missing'; echo ${a//o*a/}", "fr_interp_missing\n"},
+	{"a=foobar; echo ${a//a/} ${a///b} ${a///}", "foobr foobar foobar\n"},
 	{
 		"echo ${a:-b}; echo $a; a=; echo ${a:-b}; a=c; echo ${a:-b}",
 		"b\n\nb\nc\n",