diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index 0d9156c..9b5504b 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
@@ -123,6 +123,13 @@
 @AutoCodec
 public class RuleClass {
 
+  /**
+   * Maximum attributes per RuleClass. Current value was chosen high enough to be considered a
+   * non-breaking change for reasonable use. It was also chosen to be low enough to give significant
+   * headroom before hitting {@link AttributeContainer}'s limits.
+   */
+  private static final int MAX_ATTRIBUTES = 150;
+
   @AutoCodec
   static final Function<? super Rule, Map<String, Label>> NO_EXTERNAL_BINDINGS =
       Functions.<Map<String, Label>>constant(ImmutableMap.<String, Label>of());
@@ -775,6 +782,14 @@
     public RuleClass build(String name, String key) {
       Preconditions.checkArgument(this.name.isEmpty() || this.name.equals(name));
       type.checkName(name);
+
+      Preconditions.checkArgument(
+          attributes.size() <= MAX_ATTRIBUTES,
+          "Rule class %s declared too many attributes (%s > %s)",
+          name,
+          attributes.size(),
+          MAX_ATTRIBUTES);
+
       type.checkAttributes(attributes);
       Preconditions.checkState(
           (type == RuleClassType.ABSTRACT)
@@ -1123,10 +1138,10 @@
     }
 
     /**
-     * Builds attribute from the attribute builder and adds it to this rule
-     * class.
+     * Builds provided attribute and attaches it to this rule class.
      *
-     * @param attr attribute builder
+     * <p>Typically rule classes should only declare a handful of attributes - this expectation is
+     * enforced when the instance is built.
      */
     public <TYPE> Builder add(Attribute.Builder<TYPE> attr) {
       addAttribute(attr.build());
diff --git a/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkRuleFunctionsApi.java b/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkRuleFunctionsApi.java
index 3d2d8a8..e557592 100644
--- a/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkRuleFunctionsApi.java
+++ b/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkRuleFunctionsApi.java
@@ -134,7 +134,8 @@
                     + "implicitly added and must not be specified. Attributes "
                     + "<code>visibility</code>, <code>deprecation</code>, <code>tags</code>, "
                     + "<code>testonly</code>, and <code>features</code> are implicitly added and "
-                    + "cannot be overridden."),
+                    + "cannot be overridden. Most rules need only a handful of attributes. To "
+                    + "limit memory usage, the rule function imposes a cap on the size of attrs."),
         // TODO(bazel-team): need to give the types of these builtin attributes
         @Param(
             name = "outputs",
diff --git a/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java b/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java
index fda2f34..aedddf5 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/RuleClassTest.java
@@ -1163,4 +1163,22 @@
 
     assertThat(stringSetting.hasAttr(SKYLARK_BUILD_SETTING_DEFAULT_ATTR_NAME, LABEL)).isFalse();
   }
+
+  @Test
+  public void testBuildTooManyAttributesRejected() {
+    RuleClass.Builder builder =
+        new RuleClass.Builder("myclass", RuleClassType.NORMAL, /*skylark=*/ false)
+            .factory(DUMMY_CONFIGURED_TARGET_FACTORY)
+            .add(attr("tags", STRING_LIST));
+    for (int i = 0; i < 150; i++) {
+      builder.add(attr("attr" + i, STRING));
+    }
+
+    IllegalArgumentException expected =
+        assertThrows(IllegalArgumentException.class, builder::build);
+
+    assertThat(expected)
+        .hasMessageThat()
+        .isEqualTo("Rule class myclass declared too many attributes (151 > 150)");
+  }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
index 3feba044..594148b 100644
--- a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
@@ -27,6 +27,8 @@
 import com.google.devtools.build.lib.analysis.skylark.SkylarkRuleClassFunctions.SkylarkRuleFunction;
 import com.google.devtools.build.lib.analysis.skylark.SkylarkRuleContext;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.events.Event;
+import com.google.devtools.build.lib.events.EventKind;
 import com.google.devtools.build.lib.packages.AdvertisedProviderSet;
 import com.google.devtools.build.lib.packages.AspectParameters;
 import com.google.devtools.build.lib.packages.Attribute;
@@ -210,6 +212,27 @@
   }
 
   @Test
+  public void testRuleClassTooManyAttributes() throws Exception {
+    ev.setFailFast(false);
+
+    ImmutableList.Builder<String> linesBuilder =
+        ImmutableList.<String>builder()
+            .add("def impl(ctx): return")
+            .add("r = rule(impl, attrs = {");
+    for (int i = 0; i < 150; i++) {
+      linesBuilder.add("    'attr" + i + "': attr.int(),");
+    }
+    linesBuilder.add("})");
+
+    evalAndExport(linesBuilder.build().toArray(new String[0]));
+
+    assertThat(ev.getEventCollector()).hasSize(1);
+    Event event = ev.getEventCollector().iterator().next();
+    assertThat(event.getKind()).isEqualTo(EventKind.ERROR);
+    assertThat(event.getMessage()).contains("Rule class r declared too many attributes");
+  }
+
+  @Test
   public void testDisableDeprecatedParams() throws Exception {
     setSkylarkSemanticsOptions("--incompatible_disable_deprecated_attr_params=true");