diff --git a/packages/react-native/ReactCommon/react/renderer/css/CSSTokenizer.h b/packages/react-native/ReactCommon/react/renderer/css/CSSTokenizer.h
index c5e28c75e6e..487a09cf06e 100644
--- a/packages/react-native/ReactCommon/react/renderer/css/CSSTokenizer.h
+++ b/packages/react-native/ReactCommon/react/renderer/css/CSSTokenizer.h
@@ -163,7 +163,9 @@ class CSSTokenizer {
 
     int32_t exponentSign = 1.0;
     int32_t exponentPart = 0;
-    if (peek() == 'e' || peek() == 'E') {
+    if ((peek() == 'e' || peek() == 'E') &&
+        (isDigit(peek(1)) ||
+         ((peek(1) == '+' || peek(1) == '-') && isDigit(peek(2))))) {
       advance();
       if (peek() == '+' || peek() == '-') {
         if (peek() == '-') {
diff --git a/packages/react-native/ReactCommon/react/renderer/css/tests/CSSLengthTest.cpp b/packages/react-native/ReactCommon/react/renderer/css/tests/CSSLengthTest.cpp
index c991ba5197b..d7346c5ffc2 100644
--- a/packages/react-native/ReactCommon/react/renderer/css/tests/CSSLengthTest.cpp
+++ b/packages/react-native/ReactCommon/react/renderer/css/tests/CSSLengthTest.cpp
@@ -44,6 +44,11 @@ TEST(CSSLength, length_values) {
 
   auto pctValue = parseCSSProperty<CSSLength>("-40%");
   EXPECT_TRUE(std::holds_alternative<std::monostate>(pctValue));
+
+  auto negativeValue = parseCSSProperty<CSSLength>("-20em");
+  EXPECT_TRUE(std::holds_alternative<CSSLength>(negativeValue));
+  EXPECT_EQ(std::get<CSSLength>(negativeValue).value, -20.0f);
+  EXPECT_EQ(std::get<CSSLength>(negativeValue).unit, CSSLengthUnit::Em);
 }
 
 TEST(CSSLength, parse_constexpr) {
diff --git a/packages/react-native/ReactCommon/react/renderer/css/tests/CSSTokenizerTest.cpp b/packages/react-native/ReactCommon/react/renderer/css/tests/CSSTokenizerTest.cpp
index 3d44b58f9f4..cfcc7b59c97 100644
--- a/packages/react-native/ReactCommon/react/renderer/css/tests/CSSTokenizerTest.cpp
+++ b/packages/react-native/ReactCommon/react/renderer/css/tests/CSSTokenizerTest.cpp
@@ -112,6 +112,11 @@ TEST(CSSTokenizer, dimension_values) {
       ".3xyz",
       CSSToken{CSSTokenType::Dimension, 0.3, "xyz"},
       CSSToken{CSSTokenType::EndOfFile});
+
+  EXPECT_TOKENS(
+      "-0.5em",
+      CSSToken{CSSTokenType::Dimension, -0.5, "em"},
+      CSSToken{CSSTokenType::EndOfFile});
 }
 
 TEST(CSSTokenizer, percent_values) {