diff --git a/java-src/io/github/erdos/stencil/standalone/JsonParser.java b/java-src/io/github/erdos/stencil/standalone/JsonParser.java
index 53c8a983..e280f206 100644
--- a/java-src/io/github/erdos/stencil/standalone/JsonParser.java
+++ b/java-src/io/github/erdos/stencil/standalone/JsonParser.java
@@ -58,7 +58,7 @@ private static Object simpleParse(PushbackReader pb) throws IOException {
         } else if (c == 'n') {
             expectWord("null", pb);
             return null;
-        } else if (Character.isDigit(c)) {
+        } else if (Character.isDigit(c) || c == '+' || c == '-') {
             return readNumber(pb);
         } else {
             throw new IllegalStateException("Unexpected character: '" + c + "'");
@@ -69,7 +69,7 @@ static Number readNumber(PushbackReader pb) throws IOException {
         char[] arr = new char[128];
         int len = pb.read(arr, 0, arr.length);
 
-        assert Character.isDigit(arr[0]);
+        assert arr[0] == '+' || arr[0] == '-' || Character.isDigit(arr[0]);
 
         int i = 0;
         while (i < len && (arr[i] == '.' || arr[i] == '-' || arr[i] == 'e' || Character.isDigit(arr[i]))) {
diff --git a/java-test/io/github/erdos/stencil/standalone/JsonParserTest.java b/java-test/io/github/erdos/stencil/standalone/JsonParserTest.java
index 66501023..b57d4349 100644
--- a/java-test/io/github/erdos/stencil/standalone/JsonParserTest.java
+++ b/java-test/io/github/erdos/stencil/standalone/JsonParserTest.java
@@ -107,6 +107,25 @@ public void readNumberTest2() throws IOException {
         assertEquals((Character) 'x', (Character) (char) pbr.read());
     }
 
+    @Test
+    public void readNumberNegativeTest() throws IOException {
+        final String input = "-3";
+        PushbackReader pbr = pbr(input);
+
+        final Number result = JsonParser.readNumber(pbr);
+        assertEquals(new BigDecimal("-3"), result);
+    }
+
+    @Test
+    @SuppressWarnings("unchecked")
+    public void readMapWithNegativeValue() throws IOException {
+        String input = "{\n" + "  \"test\": -3\n" + "}";
+        PushbackReader pbr = pbr(input);
+
+        Map<String, Object> result = (Map<String, Object>) JsonParser.read(pbr);
+        assertEquals(new BigDecimal("-3"), result.get("test"));
+    }
+
     @Test
     public void readScalarsTest() throws IOException {
         assertEquals(true, JsonParser.read(pbr("true")));