diff --git a/zcl/json/parser.go b/zcl/json/parser.go
index 953092b..7e13674 100644
--- a/zcl/json/parser.go
+++ b/zcl/json/parser.go
@@ -3,6 +3,7 @@ package json
 import (
 	"encoding/json"
 	"fmt"
+	"math/big"
 
 	"github.com/apparentlymart/go-zcl/zcl"
 )
@@ -207,7 +208,41 @@ func parseArray(p *peeker) (node, zcl.Diagnostics) {
 }
 
 func parseNumber(p *peeker) (node, zcl.Diagnostics) {
-	return nil, nil
+	tok := p.Read()
+
+	// Use encoding/json to validate the number syntax.
+	// TODO: Do this more directly to produce better diagnostics.
+	var num json.Number
+	err := json.Unmarshal(tok.Bytes, &num)
+	if err != nil {
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Invalid JSON number",
+				Detail:   fmt.Sprintf("There is a syntax error in the given JSON number."),
+				Subject:  &tok.Range,
+			},
+		}
+	}
+
+	f, _, err := (&big.Float{}).Parse(string(num), 10)
+	if err != nil {
+		// Should never happen if above passed, since JSON numbers are a subset
+		// of what big.Float can parse...
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Invalid JSON number",
+				Detail:   fmt.Sprintf("There is a syntax error in the given JSON number."),
+				Subject:  &tok.Range,
+			},
+		}
+	}
+
+	return &numberVal{
+		Value:    f,
+		SrcRange: tok.Range,
+	}, nil
 }
 
 func parseString(p *peeker) (node, zcl.Diagnostics) {
diff --git a/zcl/json/parser_test.go b/zcl/json/parser_test.go
index 001dc93..78021db 100644
--- a/zcl/json/parser_test.go
+++ b/zcl/json/parser_test.go
@@ -1,6 +1,7 @@
 package json
 
 import (
+	"math/big"
 	"reflect"
 	"testing"
 
@@ -111,6 +112,82 @@ func TestParse(t *testing.T) {
 			nil,
 			1,
 		},
+		{
+			`1`,
+			&numberVal{
+				Value: mustBigFloat("1"),
+				SrcRange: zcl.Range{
+					Start: zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   zcl.Pos{Line: 1, Column: 2, Byte: 1},
+				},
+			},
+			0,
+		},
+		{
+			`1.2`,
+			&numberVal{
+				Value: mustBigFloat("1.2"),
+				SrcRange: zcl.Range{
+					Start: zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   zcl.Pos{Line: 1, Column: 4, Byte: 3},
+				},
+			},
+			0,
+		},
+		{
+			`-1`,
+			&numberVal{
+				Value: mustBigFloat("-1"),
+				SrcRange: zcl.Range{
+					Start: zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   zcl.Pos{Line: 1, Column: 3, Byte: 2},
+				},
+			},
+			0,
+		},
+		{
+			`1.2e5`,
+			&numberVal{
+				Value: mustBigFloat("120000"),
+				SrcRange: zcl.Range{
+					Start: zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   zcl.Pos{Line: 1, Column: 6, Byte: 5},
+				},
+			},
+			0,
+		},
+		{
+			`1.2e+5`,
+			&numberVal{
+				Value: mustBigFloat("120000"),
+				SrcRange: zcl.Range{
+					Start: zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   zcl.Pos{Line: 1, Column: 7, Byte: 6},
+				},
+			},
+			0,
+		},
+		{
+			`1.2e-5`,
+			&numberVal{
+				Value: mustBigFloat("1.2e-5"),
+				SrcRange: zcl.Range{
+					Start: zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   zcl.Pos{Line: 1, Column: 7, Byte: 6},
+				},
+			},
+			0,
+		},
+		{
+			`.1`,
+			nil,
+			1,
+		},
+		{
+			`+2`,
+			nil,
+			1,
+		},
 
 		// Objects
 		{
@@ -259,3 +336,11 @@ func TestParse(t *testing.T) {
 		})
 	}
 }
+
+func mustBigFloat(s string) *big.Float {
+	f, _, err := (&big.Float{}).Parse(s, 10)
+	if err != nil {
+		panic(err)
+	}
+	return f
+}