diff --git a/readthedocs/core/utils/__init__.py b/readthedocs/core/utils/__init__.py
index c257470406b..913b93dc0ce 100644
--- a/readthedocs/core/utils/__init__.py
+++ b/readthedocs/core/utils/__init__.py
@@ -19,7 +19,7 @@
 )
 from readthedocs.doc_builder.constants import DOCKER_LIMITS
 from readthedocs.projects.constants import CELERY_LOW, CELERY_MEDIUM, CELERY_HIGH
-from readthedocs.doc_builder.exceptions import BuildMaxConcurrencyError
+from readthedocs.doc_builder.exceptions import BuildMaxConcurrencyError, DuplicatedBuildError
 
 
 log = logging.getLogger(__name__)
@@ -165,8 +165,42 @@ def prepare_build(
         # External builds should be lower priority.
         options['priority'] = CELERY_LOW
 
+    skip_build = False
+    if commit:
+        skip_build = (
+            Build.objects
+            .filter(
+                project=project,
+                version=version,
+                commit=commit,
+            ).exclude(
+                state=BUILD_STATE_FINISHED,
+            ).exists()
+        )
+    else:
+        skip_build = Build.objects.filter(
+            project=project,
+            version=version,
+            state=BUILD_STATE_TRIGGERED,
+        ).count() > 0
+    if skip_build:
+        # TODO: we could mark the old build as duplicated, however we reset our
+        # position in the queue and go back to the end of it --penalization
+        log.warning(
+            'Marking build to be skipped by builder. project=%s version=%s build=%s commit=%s',
+            project.slug,
+            version.slug,
+            build.pk,
+            commit,
+        )
+        build.error = DuplicatedBuildError.message
+        build.success = False
+        build.exit_code = 1
+        build.state = BUILD_STATE_FINISHED
+        build.save()
+
     # Start the build in X minutes and mark it as limited
-    if project.has_feature(Feature.LIMIT_CONCURRENT_BUILDS):
+    if not skip_build and project.has_feature(Feature.LIMIT_CONCURRENT_BUILDS):
         running_builds = (
             Build.objects
             .filter(project__slug=project.slug)
diff --git a/readthedocs/doc_builder/exceptions.py b/readthedocs/doc_builder/exceptions.py
index d7a511430a4..32239828434 100644
--- a/readthedocs/doc_builder/exceptions.py
+++ b/readthedocs/doc_builder/exceptions.py
@@ -57,6 +57,10 @@ class BuildMaxConcurrencyError(BuildEnvironmentError):
     message = ugettext_noop('Concurrency limit reached ({limit}), retrying in 5 minutes.')
 
 
+class DuplicatedBuildError(BuildEnvironmentError):
+    message = ugettext_noop('Duplicated build.')
+
+
 class BuildEnvironmentWarning(BuildEnvironmentException):
     pass
 
diff --git a/readthedocs/projects/tasks.py b/readthedocs/projects/tasks.py
index 79df64cfb6d..2607f76ebc1 100644
--- a/readthedocs/projects/tasks.py
+++ b/readthedocs/projects/tasks.py
@@ -58,6 +58,7 @@
     BuildEnvironmentWarning,
     BuildMaxConcurrencyError,
     BuildTimeoutError,
+    DuplicatedBuildError,
     MkDocsYAMLParseError,
     ProjectBuildsSkippedError,
     VersionLockedError,
@@ -542,6 +543,16 @@ def run(
             self.commit = commit
             self.config = None
 
+            if self.build['state'] == BUILD_STATE_FINISHED and self.build['error'] == DuplicatedBuildError.message:
+                log.warning(
+                    'NOOP: build is marked as duplicated. project=%s version=%s build=%s commit=%s',
+                    self.project.slug,
+                    self.version.slug,
+                    build_pk,
+                    self.commit,
+                )
+                return True
+
             if self.project.has_feature(Feature.LIMIT_CONCURRENT_BUILDS):
                 response = api_v2.build.running.get(project__slug=self.project.slug)
                 builds_running = response.get('count', 0)