diff --git a/src/bun.js/RuntimeTranspilerCache.zig b/src/bun.js/RuntimeTranspilerCache.zig
index cee2ec7c33..512c9fb746 100644
--- a/src/bun.js/RuntimeTranspilerCache.zig
+++ b/src/bun.js/RuntimeTranspilerCache.zig
@@ -1,8 +1,10 @@
+// ** Update the version number when any breaking changes are made to the cache format or to the JS parser **
+const expected_version = 1;
+
 const bun = @import("root").bun;
 const std = @import("std");
 const Output = bun.Output;
 const JSC = bun.JSC;
-const expected_version = 1;
 
 const debug = Output.scoped(.cache, false);
 const MINIMUM_CACHE_SIZE = 50 * 1024;
diff --git a/src/bun.js/bindings/JSEnvironmentVariableMap.cpp b/src/bun.js/bindings/JSEnvironmentVariableMap.cpp
index abf794786c..b23eac87d0 100644
--- a/src/bun.js/bindings/JSEnvironmentVariableMap.cpp
+++ b/src/bun.js/bindings/JSEnvironmentVariableMap.cpp
@@ -135,7 +135,26 @@ JSValue createEnvironmentVariablesMap(Zig::GlobalObject* globalObject)
             hasTZ = true;
             continue;
         }
-        object->putDirectCustomAccessor(vm, Identifier::fromString(vm, name), JSC::CustomGetterSetter::create(vm, jsGetterEnvironmentVariable, jsSetterEnvironmentVariable), JSC::PropertyAttribute::CustomAccessor | 0);
+        ASSERT(len > 0);
+
+        Identifier identifier = Identifier::fromString(vm, name);
+
+        // CustomGetterSetter doesn't support indexed properties yet.
+        // This causes strange issues when the environment variable name is an integer.
+        if (UNLIKELY(chars[0] >= '0' && chars[0] <= '9')) {
+            if (auto index = parseIndex(identifier)) {
+                ZigString valueString = { nullptr, 0 };
+                ZigString nameStr = toZigString(name);
+                JSValue value = jsUndefined();
+                if (Bun__getEnvValue(globalObject, &nameStr, &valueString)) {
+                    value = jsString(vm, Zig::toStringCopy(valueString));
+                }
+                object->putDirectIndex(globalObject, *index, value, 0, PutDirectIndexLikePutDirect);
+                continue;
+            }
+        }
+
+        object->putDirectCustomAccessor(vm, identifier, JSC::CustomGetterSetter::create(vm, jsGetterEnvironmentVariable, jsSetterEnvironmentVariable), JSC::PropertyAttribute::CustomAccessor | 0);
     }
 
     unsigned int TZAttrs = JSC::PropertyAttribute::CustomAccessor | 0;
diff --git a/src/js_parser.zig b/src/js_parser.zig
index acd2201f0f..e25c4c109e 100644
--- a/src/js_parser.zig
+++ b/src/js_parser.zig
@@ -1,3 +1,7 @@
+/// ** IMPORTANT **
+/// ** When making changes to the JavaScript Parser that impact runtime behavior or fix bugs **
+/// ** you must also increment the `expected_version` in RuntimeTranspilerCache.zig **
+/// ** IMPORTANT **
 pub const std = @import("std");
 pub const logger = @import("root").bun.logger;
 pub const js_lexer = bun.js_lexer;