diff --git a/lib/source-map-consumer.js b/lib/source-map-consumer.js
index ea32f43e..e09b5b1b 100644
--- a/lib/source-map-consumer.js
+++ b/lib/source-map-consumer.js
@@ -966,14 +966,22 @@ BasicSourceMapConsumer.prototype.computeColumnSpans =
  */
 BasicSourceMapConsumer.prototype.originalPositionFor =
   function SourceMapConsumer_originalPositionFor(aArgs) {
-    var needleLine = util.getArg(aArgs, 'line');
-    var needleColumn = util.getArg(aArgs, 'column');
-    // The legacy code path went through `_findMapping` which validated
-    // line/column at the entry. Slab-direct lookups bypass that, so
-    // we have to validate explicitly to keep the documented errors.
+    // Inline the optional read for required args — every trace call paid
+    // for a `getArg` function call plus an `'in' in aArgs` check. Combining
+    // the value validation with a `typeof !== 'number'` guard preserves the
+    // documented "is a required argument" error for missing/undefined args
+    // while skipping the function-call overhead.
+    var needleLine = aArgs.line;
+    var needleColumn = aArgs.column;
+    if (typeof needleLine !== 'number') {
+      throw new Error('"line" is a required argument.');
+    }
     if (needleLine <= 0) {
       throw new TypeError('Line must be greater than or equal to 1, got ' + needleLine);
     }
+    if (typeof needleColumn !== 'number') {
+      throw new Error('"column" is a required argument.');
+    }
     if (needleColumn < 0) {
       throw new TypeError('Column must be greater than or equal to 0, got ' + needleColumn);
     }
@@ -1202,11 +1210,18 @@ BasicSourceMapConsumer.prototype.generatedPositionFor =
       };
     }
 
-    var needleLine = util.getArg(aArgs, 'line');
-    var needleColumn = util.getArg(aArgs, 'column');
+    // Inline the required-arg reads — same pattern as originalPositionFor.
+    var needleLine = aArgs.line;
+    var needleColumn = aArgs.column;
+    if (typeof needleLine !== 'number') {
+      throw new Error('"line" is a required argument.');
+    }
     if (needleLine <= 0) {
       throw new TypeError('Line must be greater than or equal to 1, got ' + needleLine);
     }
+    if (typeof needleColumn !== 'number') {
+      throw new Error('"column" is a required argument.');
+    }
     if (needleColumn < 0) {
       throw new TypeError('Column must be greater than or equal to 0, got ' + needleColumn);
     }