diff --git a/internal/generator/constexpr.go b/internal/generator/constexpr.go
index 28a3a60..c7d7d6a 100644
--- a/internal/generator/constexpr.go
+++ b/internal/generator/constexpr.go
@@ -5,14 +5,17 @@ import (
 	"go/ast"
 	"go/constant"
 	"go/token"
-	"math/big"
 	"strconv"
 	"unicode/utf8"
 )
 
-// maxShiftLeft caps a left shift so a malformed source can't ask for an enormous allocation. a right
-// shift needs no cap, shifting past the width of a value settles at 0 or -1.
-const maxShiftLeft = 512
+const (
+	// maxShiftLeft caps a left shift so a malformed source can't ask for an enormous allocation
+	maxShiftLeft = 512
+	// maxShiftRight bounds a right shift count, which only has to reach past the width of the value;
+	// no constant comes near it, and it keeps the count in range of uint
+	maxShiftRight = 1 << 20
+)
 
 // intTypeInfo describes the width and signedness of a builtin integer type
 type intTypeInfo struct {
@@ -357,11 +360,9 @@ func (r *constResolver) evalShift(e *ast.BinaryExpr, x typedValue, iotaVal int64
 	switch {
 	case e.Op == token.SHL && (!exact || count > maxShiftLeft):
 		return typedValue{}, fmt.Errorf("shift count %s is too large", y.ExactString())
-	case e.Op == token.SHR:
-		// a shift wider than the value itself keeps its result, clamp it to stay in range of uint
-		if width := bitLen(xv) + 1; !exact || count > width {
-			count = width
-		}
+	case e.Op == token.SHR && (!exact || count > maxShiftRight):
+		// shifting further than the value is wide keeps giving the same result
+		count = maxShiftRight
 	}
 	return typedValue{value: constant.Shift(xv, e.Op, uint(count)), typ: x.typ}, nil
 }
@@ -431,7 +432,7 @@ func (r *constResolver) evalMinMax(e *ast.CallExpr, name string, iotaVal int64)
 	}
 
 	var best typedValue
-	typ := ""
+	typ, anyFloat := "", false
 	for i, arg := range e.Args {
 		v, err := r.eval(arg, iotaVal)
 		if err != nil {
@@ -443,14 +444,19 @@ func (r *constResolver) evalMinMax(e *ast.CallExpr, name string, iotaVal int64)
 		if typ == "" {
 			typ = v.typ // a typed argument gives the result its type
 		}
+		anyFloat = anyFloat || v.value.Kind() == constant.Float
 		if i == 0 || constant.Compare(v.value, op, best.value) {
 			best = v
 		}
 	}
-	if typ == "" {
-		return best, nil
+	if typ != "" {
+		return r.convert(best, typ)
+	}
+	if anyFloat {
+		// an untyped float argument makes the result untyped float, whichever argument won
+		return typedValue{value: constant.ToFloat(best.value)}, nil
 	}
-	return r.convert(best, typ)
+	return best, nil
 }
 
 // roundFloat drops the precision a float type cannot hold, the compiler stores a typed float
@@ -464,18 +470,6 @@ func roundFloat(v constant.Value, typ string) constant.Value {
 	return constant.MakeFloat64(f)
 }
 
-// bitLen is the number of bits an integer value occupies
-func bitLen(v constant.Value) uint64 {
-	i, ok := constant.Val(v).(*big.Int)
-	if !ok {
-		return 64 // anything go/constant keeps as an int64
-	}
-	if n := i.BitLen(); n > 0 {
-		return uint64(n)
-	}
-	return 0
-}
-
 // unparen strips the parentheses around an expression
 func unparen(expr ast.Expr) ast.Expr {
 	for {
@@ -524,13 +518,7 @@ func (r *constResolver) convert(v typedValue, typ string) (typedValue, error) {
 // the language allows
 func literalValue(lit *ast.BasicLit) (constant.Value, error) {
 	switch lit.Kind {
-	case token.INT, token.FLOAT:
-		v := constant.MakeFromLiteral(lit.Value, lit.Kind, 0)
-		if v.Kind() == constant.Unknown {
-			return nil, fmt.Errorf("invalid literal %s", lit.Value)
-		}
-		return v, nil
-	case token.STRING:
+	case token.INT, token.FLOAT, token.STRING:
 		v := constant.MakeFromLiteral(lit.Value, lit.Kind, 0)
 		if v.Kind() == constant.Unknown {
 			return nil, fmt.Errorf("invalid literal %s", lit.Value)
diff --git a/internal/generator/constexpr_test.go b/internal/generator/constexpr_test.go
index d90aef6..5d31951 100644
--- a/internal/generator/constexpr_test.go
+++ b/internal/generator/constexpr_test.go
@@ -98,6 +98,13 @@ func TestConstResolverValues(t *testing.T) {
 		{"string of a code point", `len(string(0x100))`, "2"},
 		{"min of a typed argument", "^max(2, uint8(1))", "253"},
 		{"max of a typed argument", "min(uint8(7), 9) + 1", "8"},
+		{"max with an untyped float", "max(5, 4.0) / 2 * 10", "25"},
+		{"min with an untyped float", "min(5, 6.0) / 2 * 10", "25"},
+		{"max of integers only", "max(5, 4) / 2 * 10", "20"},
+		{"string of a value out of range", "len(string(-1))", "3"},
+		{"shift right of a wide value", "1<<70 >> 2000", "0"},
+		// the compiler rejects a shift count this large outright, the result is still 0
+		{"shift right past the bound", "1 >> 2000000", "0"},
 	}
 
 	for _, tt := range tests {
@@ -136,6 +143,29 @@ func TestConstResolverErrors(t *testing.T) {
 		{"comparison operator", "const x = 1 < 2", "unsupported binary operator"},
 		{"self reference", "const x = x + 1", "refers to itself"},
 		{"reference cycle", "const (\n\tx = y\n\ty = x\n)", "refers to itself"},
+		{"failing operand of a negation", "const x = -missing", "unknown constant missing"},
+		{"complement of a string", `const x = ^"str"`, "not an integer"},
+		{"failing right operand", "const x = 1 + missing", "unknown constant missing"},
+		{"operand out of range for the type", "const x = uint8(1) + 300", "overflows uint8"},
+		{"string added to a number", `const x = 1 + "s"`, "not a number"},
+		{"number added to a string", `const x = "s" + 1`, "not a number"},
+		{"fractional remainder", "const x = 1.5 % 2", "not an integer"},
+		{"remainder by a fraction", "const x = 2 % 1.5", "not an integer"},
+		{"shift of a string", `const x = "s" << 1`, "not an integer"},
+		{"failing shift count", "const x = 1 << missing", "unknown constant missing"},
+		{"fractional shift count", "const x = 1 << 1.5", "not an integer"},
+		{"conversion with two arguments", "const x = uint8(1, 2)", "unsupported call expression"},
+		{"min without arguments", "const x = min()", "at least one argument"},
+		{"failing min argument", "const x = min(missing, 1)", "unknown constant missing"},
+		{"min of a string", `const x = min("a", 1)`, "not a number"},
+		{"failing len argument", "const x = len(missing)", "unknown constant missing"},
+		{"failing conversion argument", "const x = uint8(missing)", "unknown constant missing"},
+		{"fractional conversion", "const x = uint8(1.5)", "not an integer"},
+		{"float conversion of a string", `const x = float64("s")`, "not a number"},
+		{"string conversion of a fraction", "const (\n\tx = str(1.5)\n)\ntype str string", "not a string"},
+		{"call of an expression", "const x = (1 + 1)(2)", "unsupported call expression"},
+		{"failing left operand of a typed sum", "const x = 300 + uint8(1)", "overflows uint8"},
+		{"alias cycle", "const x = ^a(0)\ntype a = b\ntype b = a", "unsupported call to a"},
 	}
 
 	for _, tt := range tests {
@@ -322,6 +352,27 @@ func TestCheckIntRange(t *testing.T) {
 	}
 }
 
+func TestConstResolverDeclarations(t *testing.T) {
+	// a name declared twice keeps the first declaration, which is what a compiling package has
+	v, err := resolveSrc(t, "package p\nconst x = 1\nconst x = 2\n", "x")
+	require.NoError(t, err)
+	assert.Equal(t, "1", v.ExactString())
+
+	// specs that are not value or type declarations are skipped
+	r := newConstResolver()
+	r.addFile(&ast.File{
+		Name: &ast.Ident{Name: "p"},
+		Decls: []ast.Decl{
+			&ast.GenDecl{Tok: token.TYPE, Specs: []ast.Spec{&ast.ImportSpec{}}},
+			&ast.GenDecl{Tok: token.CONST, Specs: []ast.Spec{&ast.ImportSpec{}}},
+			&ast.GenDecl{Tok: token.IMPORT, Specs: []ast.Spec{&ast.ImportSpec{}}},
+			&ast.FuncDecl{Name: &ast.Ident{Name: "f"}},
+		},
+	})
+	assert.Empty(t, r.decls)
+	assert.Empty(t, r.types)
+}
+
 func TestConstResolverUnsupportedNodes(t *testing.T) {
 	r := newConstResolver()
 
@@ -345,6 +396,18 @@ func TestConstResolverUnsupportedNodes(t *testing.T) {
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "not a number")
 
+	for _, lit := range []*ast.BasicLit{
+		{Kind: token.INT, Value: "12abc"},
+		{Kind: token.FLOAT, Value: "1.2.3"},
+		{Kind: token.CHAR, Value: "'"},
+		{Kind: token.CHAR, Value: "abc"},
+		{Kind: token.CHAR, Value: `'\q'`},
+	} {
+		_, err = literalValue(lit)
+		require.Error(t, err, lit.Value)
+		assert.Contains(t, err.Error(), "invalid literal", lit.Value)
+	}
+
 	_, err = r.resolve("nothing")
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "unknown constant nothing")
@@ -472,6 +535,32 @@ const (
 	assert.Contains(t, err.Error(), "const codeB: value -1 is negative but the type is uint8")
 }
 
+func TestParseUntypedValueOutOfRange(t *testing.T) {
+	// a constant without a type of its own still has to fit the underlying type of the enum
+	src := `package test
+type small int8
+const (
+	smallA small = 100
+	smallB       = 200
+)
+`
+	_, err := parseSrc(t, "small", src)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "const smallB: value 200 overflows int8")
+}
+
+func TestParseConstWithoutValue(t *testing.T) {
+	src := `package test
+type status int
+const (
+	statusA
+)
+`
+	_, err := parseSrc(t, "status", src)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "no value for const statusA")
+}
+
 func TestParseValueOutOfRange(t *testing.T) {
 	src := `package test
 type small int8
diff --git a/internal/generator/generator_test.go b/internal/generator/generator_test.go
index f09c2b7..a3b4c0d 100644
--- a/internal/generator/generator_test.go
+++ b/internal/generator/generator_test.go
@@ -1449,6 +1449,7 @@ func TestParseAliasComment(t *testing.T) {
 		{"multiple aliases", "// enum:alias=rw,read-write", []string{"rw", "read-write"}},
 		{"with whitespace", "// enum:alias= rw , read-write ", []string{"rw", "read-write"}},
 		{"empty value", "// enum:alias=", nil},
+		{"only separators", "// enum:alias=,,", nil},
 		{"empty between commas", "// enum:alias=a,,b", []string{"a", "b"}},
 		{"no alias directive", "// some comment", nil},
 		{"nil comment", "", nil},