diff --git a/.gitignore b/.gitignore
index ea5182ac1..f2086c0a3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,6 @@
 
 # Appraisals
 instrumentation/**/*.gemfile.lock
+
+# Vendored gems
+**/vendor/**/*
diff --git a/sdk/lib/opentelemetry/sdk/trace/samplers/probability_sampler.rb b/sdk/lib/opentelemetry/sdk/trace/samplers/probability_sampler.rb
index 5e1359b1d..1f872b1d3 100644
--- a/sdk/lib/opentelemetry/sdk/trace/samplers/probability_sampler.rb
+++ b/sdk/lib/opentelemetry/sdk/trace/samplers/probability_sampler.rb
@@ -16,7 +16,7 @@ class ProbabilitySampler
 
           def initialize(probability, ignore_parent:, apply_to_remote_parent:, apply_to_all_spans:)
             @probability = probability
-            @id_upper_bound = format('%016x', (probability * (2**64 - 1)).ceil)
+            @id_upper_bound = (probability * (2**64 - 1)).ceil
             @use_parent_sampled_flag = !ignore_parent
             @apply_to_remote_parent = apply_to_remote_parent
             @apply_to_all_spans = apply_to_all_spans
@@ -55,7 +55,7 @@ def sample_trace_id_for_child?(parent_context, trace_id)
           end
 
           def sample_trace_id?(trace_id)
-            @probability == 1.0 || trace_id[16, 16] < @id_upper_bound
+            @probability == 1.0 || trace_id[8, 8].unpack1('Q>') < @id_upper_bound
           end
         end
       end
diff --git a/sdk/test/opentelemetry/sdk/trace/samplers_test.rb b/sdk/test/opentelemetry/sdk/trace/samplers_test.rb
index f57580ea1..3fc38df4d 100644
--- a/sdk/test/opentelemetry/sdk/trace/samplers_test.rb
+++ b/sdk/test/opentelemetry/sdk/trace/samplers_test.rb
@@ -160,7 +160,9 @@
   end
 
   def trace_id(id)
-    format('%032x', id)
+    first = id >> 64
+    second = id & 0xffff_ffff_ffff_ffff
+    [first, second].pack('Q>Q>')
   end
 
   def call_sampler(sampler, trace_id: nil, parent_context: nil, links: nil, name: nil, kind: nil, attributes: nil)