diff --git a/lib/prometheus/client/gauge.rb b/lib/prometheus/client/gauge.rb
index f7990427..f2542ad4 100644
--- a/lib/prometheus/client/gauge.rb
+++ b/lib/prometheus/client/gauge.rb
@@ -13,6 +13,10 @@ def type
 
       # Sets the value for the given label set
       def set(labels, value)
+        unless value.is_a?(Numeric)
+          raise ArgumentError, 'value must be a number'
+        end
+
         @values[label_set_for(labels)] = value
       end
     end
diff --git a/spec/prometheus/client/gauge_spec.rb b/spec/prometheus/client/gauge_spec.rb
index 9f2381f4..665d9fe9 100644
--- a/spec/prometheus/client/gauge_spec.rb
+++ b/spec/prometheus/client/gauge_spec.rb
@@ -24,5 +24,13 @@
         end.to change { gauge.get(test: 'value') }.from(nil).to(42)
       end.to_not change { gauge.get }
     end
+
+    context 'given an invalid value' do
+      it 'raises an ArgumentError' do
+        expect do
+          gauge.set({}, nil)
+        end.to raise_exception(ArgumentError)
+      end
+    end
   end
 end