diff --git a/CHANGELOG.md b/CHANGELOG.md
index e59c2ee5..bad58237 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,7 @@ Other new features:
   * When zooming to fit, constraints are also considered.
   * When selecting a point and a line, projected distance to to current
     workplane is displayed.
+  * In expressions, numbers can contain the digit group separator, "_".
   * The "=" key is bound to "Zoom In", like "+" key.
   * The numpad decimal separator key is bound to "." regardless of locale.
 
diff --git a/src/expr.cpp b/src/expr.cpp
index e00a1143..7bc2cf5d 100644
--- a/src/expr.cpp
+++ b/src/expr.cpp
@@ -612,7 +612,6 @@ public:
     char ReadChar();
     char PeekChar();
 
-    double ReadNumber();
     std::string ReadWord();
     void SkipSpace();
 
@@ -620,6 +619,7 @@ public:
     Token PopOperand(std::string *error);
 
     int Precedence(Token token);
+    Token LexNumber(std::string *error);
     Token Lex(std::string *error);
     bool Reduce(std::string *error);
     bool Parse(std::string *error, size_t reduceUntil = 0);
@@ -650,14 +650,6 @@ char ExprParser::PeekChar() {
     return input[inputPos];
 }
 
-double ExprParser::ReadNumber() {
-    char *endptr;
-    double d = strtod(input + inputPos, &endptr);
-    unsigned len = endptr - (input + inputPos);
-    inputPos += len;
-    return d;
-}
-
 std::string ExprParser::ReadWord() {
     std::string s;
 
@@ -676,6 +668,31 @@ void ExprParser::SkipSpace() {
     }
 }
 
+ExprParser::Token ExprParser::LexNumber(std::string *error) {
+    std::string s;
+
+    while(char c = PeekChar()) {
+        if(!((c >= '0' && c <= '9') || c == 'e' || c == 'E' || c == '.' || c == '_')) break;
+        if(c == '_') {
+            ReadChar();
+            continue;
+        }
+        s.push_back(ReadChar());
+    }
+
+    char *endptr;
+    double d = strtod(s.c_str(), &endptr);
+
+    Token t = Token::From();
+    if(endptr == &*s.end()) {
+        t = Token::From(TokenType::OPERAND, Expr::Op::CONSTANT);
+        t.expr->v = d;
+    } else {
+        *error = "'" + s + "' is not a valid number";
+    }
+    return t;
+}
+
 ExprParser::Token ExprParser::Lex(std::string *error) {
     SkipSpace();
 
@@ -705,9 +722,7 @@ ExprParser::Token ExprParser::Lex(std::string *error) {
             *error = "'" + s + "' is not a valid variable, function or constant";
         }
     } else if(isdigit(c) || c == '.') {
-        double d = ReadNumber();
-        t = Token::From(TokenType::OPERAND, Expr::Op::CONSTANT);
-        t.expr->v = d;
+        return LexNumber(error);
     } else if(ispunct(c)) {
         ReadChar();
         if(c == '+') {
diff --git a/test/core/expr/test.cpp b/test/core/expr/test.cpp
index ab3829b5..8ae4c757 100644
--- a/test/core/expr/test.cpp
+++ b/test/core/expr/test.cpp
@@ -26,6 +26,8 @@ TEST_CASE(literal) {
   CHECK_TRUE(e->Eval() == 42);
   CHECK_PARSE(e, "42.5");
   CHECK_TRUE(e->Eval() == 42.5);
+  CHECK_PARSE(e, "1_000_000");
+  CHECK_TRUE(e->Eval() == 1000000);
 }
 
 TEST_CASE(unary_ops) {
@@ -95,6 +97,8 @@ TEST_CASE(errors) {
                   "Unexpected character");
   CHECK_PARSE_ERR("notavar",
                   "'notavar' is not a valid variable, function or constant");
+  CHECK_PARSE_ERR("1e2e3",
+                  "'1e2e3' is not a valid number");
   CHECK_PARSE_ERR("_",
                   "'_' is not a valid operator");
   CHECK_PARSE_ERR("2 2",