diff --git a/examples/wallet/wallet.vy b/examples/wallet/wallet.vy
index 7e92c7e89c..3c970d4401 100644
--- a/examples/wallet/wallet.vy
+++ b/examples/wallet/wallet.vy
@@ -63,7 +63,7 @@ def approve(_seq: int128, to: address, _value: uint256, data: Bytes[4096], sigda
     # Increase the number of approved transactions by 1
     self.seq += 1
     # Use raw_call to send the transaction
-    return raw_call(to, data, max_outsize=4096, gas=3000000, value=_value)
+    return raw_call(to, data, max_outsize=4096, gas=3_000_000, value=_value)
 
 
 @external
diff --git a/tests/functional/grammar/test_grammar.py b/tests/functional/grammar/test_grammar.py
index de399e84b7..3b498707f6 100644
--- a/tests/functional/grammar/test_grammar.py
+++ b/tests/functional/grammar/test_grammar.py
@@ -20,7 +20,7 @@ def test_basic_grammar():
     code_func = """
     @external
     def one_two_three() -> uint256:
-        return 123123123
+        return 123_123_123
     """
 
     assert parse_vyper_source(code, dedent=True)
diff --git a/vyper/ast/grammar.lark b/vyper/ast/grammar.lark
index 3feb4df92f..1ed606d455 100644
--- a/vyper/ast/grammar.lark
+++ b/vyper/ast/grammar.lark
@@ -321,11 +321,11 @@ _NEWLINE: ( /\r?\n[\t ]*/ | COMMENT )+
 STRING: /b?("(?!"").*?(?<!\\)(\\\\)*?"|'(?!'').*?(?<!\\)(\\\\)*?')/i
 DOCSTRING: /(""".*?(?<!\\)(\\\\)*?"""|'''.*?(?<!\\)(\\\\)*?''')/is
 
-DEC_NUMBER: /0|[1-9]\d*/i
+DEC_NUMBER: /0|[1-9]([0-9]*_)?([0-9]+_)*[0-9]+/
 HEX_NUMBER.2: /0x[\da-f]*/i
-OCT_NUMBER.2: /0o[0-7]*/i
+OCT_NUMBER.2: /0o([0-7]+_)*[0-7]+/
 BIN_NUMBER.2 : /0b[0-1]*/i
-FLOAT_NUMBER.2: /((\d+\.\d*|\.\d+)(e[-+]?\d+)?|\d+(e[-+]?\d+))/i
+FLOAT_NUMBER.2: /((\d+(_\d+)*\.\d*|\.\d+)(e[-+]?\d+)?|\d+(_\d+)*(e[-+]?\d+)?)/i
 
 _number: DEC_NUMBER
        | HEX_NUMBER