diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9e30aea9..f6bff536 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,14 @@
+# 1.5.1 (Unreleased)
+
+* `function/stdlib`: The `merge` function will no longer panic if all given maps are empty. ([#58](https://github.com/zclconf/go-cty/pull/58))
+* `function/stdlib`: The various set-manipulation functions, like `setunion`, will no longer panic if given an unknown set value. ([#59](https://github.com/zclconf/go-cty/pull/59))
+
 # 1.5.0 (March 17, 2025)
 
 * `cty`: New `Value.HasWhollyKnownType` method, for testing whether a value's type could potentially change if any unknown values it was constructed from were to become known. ([#55](https://github.com/zclconf/go-cty/pull/55))
 * `convert`: Fix incorrect panic when converting a tuple with a dynamic-typed null member into a list or set, due to overly-liberal type unification. ([#56](https://github.com/zclconf/go-cty/pull/56))
 
-# 1.4.2 (Unreleased)
+# 1.4.2
 
 * `function/stdlib`: The `jsonencode` function will now correctly accept a null as its argument, and produce the JSON representation `"null"` rather than returning an error. ([#54](https://github.com/zclconf/go-cty/pull/54))
 * `convert`: Don't panic when asked to convert a tuple of objects to a list type constraint containing a nested `cty.DynamicPseudoType`. ([#53](https://github.com/zclconf/go-cty/pull/53))
diff --git a/cty/function/stdlib/collection.go b/cty/function/stdlib/collection.go
index a2d1349a..cfa8c94c 100644
--- a/cty/function/stdlib/collection.go
+++ b/cty/function/stdlib/collection.go
@@ -762,6 +762,9 @@ var MergeFunc = function.New(&function.Spec{
 		case allNull:
 			return cty.NullVal(retType), nil
 		case retType.IsMapType():
+			if len(outputMap) == 0 {
+				return cty.MapValEmpty(retType.ElementType()), nil
+			}
 			return cty.MapVal(outputMap), nil
 		case retType.IsObjectType(), retType.Equals(cty.DynamicPseudoType):
 			return cty.ObjectVal(outputMap), nil
diff --git a/cty/function/stdlib/collection_test.go b/cty/function/stdlib/collection_test.go
index 96c1c89d..f2dd4f26 100644
--- a/cty/function/stdlib/collection_test.go
+++ b/cty/function/stdlib/collection_test.go
@@ -506,6 +506,14 @@ func TestMerge(t *testing.T) {
 			cty.NilVal,
 			true,
 		},
+		{ // Empty maps are allowed in merge
+			[]cty.Value{
+				cty.MapValEmpty(cty.String),
+				cty.MapValEmpty(cty.String),
+			},
+			cty.MapValEmpty(cty.String),
+			false,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/cty/function/stdlib/set.go b/cty/function/stdlib/set.go
index f24b5f29..6e3e5ae6 100644
--- a/cty/function/stdlib/set.go
+++ b/cty/function/stdlib/set.go
@@ -167,7 +167,7 @@ func setOperationReturnType(args []cty.Value) (ret cty.Type, err error) {
 
 		// Do not unify types for empty dynamic pseudo typed collections. These
 		// will always convert to any other concrete type.
-		if arg.LengthInt() == 0 && ty.Equals(cty.DynamicPseudoType) {
+		if arg.IsKnown() && arg.LengthInt() == 0 && ty.Equals(cty.DynamicPseudoType) {
 			continue
 		}
 
diff --git a/cty/function/stdlib/set_test.go b/cty/function/stdlib/set_test.go
index 34494da5..a9af3fbb 100644
--- a/cty/function/stdlib/set_test.go
+++ b/cty/function/stdlib/set_test.go
@@ -76,6 +76,13 @@ func TestSetUnion(t *testing.T) {
 			},
 			cty.SetValEmpty(cty.DynamicPseudoType),
 		},
+		{
+			[]cty.Value{
+				cty.SetVal([]cty.Value{cty.StringVal("5")}),
+				cty.UnknownVal(cty.Set(cty.Number)),
+			},
+			cty.UnknownVal(cty.Set(cty.String)),
+		},
 	}
 
 	for _, test := range tests {
@@ -159,6 +166,13 @@ func TestSetIntersection(t *testing.T) {
 			},
 			cty.SetValEmpty(cty.DynamicPseudoType),
 		},
+		{
+			[]cty.Value{
+				cty.SetVal([]cty.Value{cty.StringVal("5")}),
+				cty.UnknownVal(cty.Set(cty.Number)),
+			},
+			cty.UnknownVal(cty.Set(cty.String)),
+		},
 	}
 
 	for _, test := range tests {
@@ -226,6 +240,11 @@ func TestSetSubtract(t *testing.T) {
 			cty.SetValEmpty(cty.DynamicPseudoType),
 			cty.SetValEmpty(cty.DynamicPseudoType),
 		},
+		{
+			cty.SetVal([]cty.Value{cty.StringVal("5")}),
+			cty.UnknownVal(cty.Set(cty.Number)),
+			cty.UnknownVal(cty.Set(cty.String)),
+		},
 	}
 
 	for _, test := range tests {
diff --git a/go.mod b/go.mod
index 882066f0..9cdd5f46 100644
--- a/go.mod
+++ b/go.mod
@@ -6,8 +6,6 @@ require (
 	github.com/google/go-cmp v0.3.1
 	github.com/kr/pretty v0.1.0 // indirect
 	github.com/vmihailenco/msgpack v3.3.3+incompatible
-	golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3 // indirect
-	golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f // indirect
 	golang.org/x/text v0.3.8
 	google.golang.org/appengine v1.1.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
diff --git a/go.sum b/go.sum
index 02310483..5773695f 100644
--- a/go.sum
+++ b/go.sum
@@ -11,16 +11,33 @@ github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/vmihailenco/msgpack v3.3.3+incompatible h1:wapg9xDUZDzGCNFlwc5SqI1rvcciqcxEHac4CYj89xI=
 github.com/vmihailenco/msgpack v3.3.3+incompatible/go.mod h1:fy3FlTQTDXWkZ7Bh6AcGMlsjHatGryHQYUTf1ShIgkk=
+github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3 h1:0GoQqolDA55aaLxZyTzK/Y2ePZzZTUrRacwib7cNsYQ=
-golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f h1:wMNYb4v58l5UBM7MYRLPG6ZhfOqbKu7X5eyFl8ZhKvA=
-golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
+golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
+golang.org/x/net v0.0.0-20220722155237-a158d28d115b h1:PxfKdU9lEEDYjdIzOtC4qFWgkU2rGHdKlKowJSMN9h0=
+golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4 h1:uVc8UZUe6tr40fFVnUP5Oj+veunVezqYl9z7DYw9xzw=
+golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
+golang.org/x/text v0.3.8 h1:nAL+RVCQ9uMn3vJZbV+MRnydTJFPf8qqY42YiA6MrqY=
+golang.org/x/text v0.3.8/go.mod h1:E6s5w1FMmriuDzIBO73fBruAKo1PCIq6d2Q6DHfQ8WQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/appengine v1.1.0 h1:igQkv0AAhEIvTEpD5LIpAfav2eeVO9HBTjvKHVJPRSs=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=