diff --git a/Makefile.am b/Makefile.am
index d3eeaddaf4..908c48b4ef 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -597,6 +597,7 @@ SCM_TESTS =					\
   tests/size.scm				\
   tests/status.scm				\
   tests/store-database.scm			\
+  tests/store-deadlock.scm			\
   tests/store-deduplication.scm		\
   tests/store-roots.scm			\
   tests/store.scm				\
diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 43a8a37184..edd01bab34 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -1200,6 +1200,7 @@ void DerivationGoal::tryToBuild()
     if (buildMode != bmCheck && validPaths.size() == drv.outputs.size()) {
         debug(format("skipping build of derivation `%1%', someone beat us to it") % drvPath);
         outputLocks.setDeletion(true);
+        outputLocks.unlock();
         done(BuildResult::AlreadyValid);
         return;
     }
@@ -3070,6 +3071,7 @@ void SubstitutionGoal::tryToRun()
     if (!repair && worker.store.isValidPath(storePath)) {
         debug(format("store path `%1%' has become valid") % storePath);
         outputLock->setDeletion(true);
+        outputLock.reset();
         amDone(ecSuccess);
         return;
     }
diff --git a/tests/store-deadlock.scm b/tests/store-deadlock.scm
new file mode 100644
index 0000000000..e960448133
--- /dev/null
+++ b/tests/store-deadlock.scm
@@ -0,0 +1,90 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2024 Reepca Russelstein <reepca@russelstein.xyz>
+;;; Copyright © 2024 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-store-deadlock)
+  #:use-module (guix tests)
+  #:use-module (guix store)
+  #:use-module (guix derivations)
+  #:use-module (guix gexp)
+  #:use-module (guix monads)
+  #:use-module (gnu packages bootstrap)
+  #:use-module (ice-9 threads)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-64))
+
+(define input-drvs
+  (map (lambda (n)
+         (computed-file (string-append "drv" (number->string n))
+                        #~(begin
+                            #$(random-text)
+                            (sleep 4)
+                            (mkdir #$output))
+                        #:guile %bootstrap-guile))
+       (iota 15)))
+
+(define top-drv
+  (computed-file "top-drv"
+                 #~(begin
+                     #$(random-text)
+                     (sleep 3)
+                     (pk 'deps: #$@input-drvs)
+                     (mkdir #$output))
+                 #:guile %bootstrap-guile))
+
+(%graft? #f)
+
+
+(test-begin "store-deadlock")
+
+(test-equal "no deadlock"                   ;https://issues.guix.gnu.org/31785
+  '(thread1 thread2 thread3)
+
+  ;; This test checks for the absence of a deadlock when guix-daemon spawns
+  ;; several child processes (one for each client) that compete to build the
+  ;; same set of derivations.  See <https://issues.guix.gnu.org/31785>.
+  (let* ((drvs (cons top-drv input-drvs))
+         (builder (lambda (name lst)
+                    (call-with-new-thread
+                     (lambda ()
+                       (with-store store
+                         (set-build-options store
+                                            #:verbosity 3
+                                            #:max-build-jobs 1)
+                         (run-with-store store
+                           (mlet %store-monad ((lst (mapm %store-monad
+                                                          lower-object lst)))
+                             (mbegin %store-monad
+                               (built-derivations lst)
+                               (return name)))))))))
+         (thread1 (builder 'thread1 drvs))
+         (thread2 (begin
+                    (sleep 1)
+                    (builder 'thread2 drvs)))
+         (thread3 (begin
+                    (sleep 1)
+                    (builder 'thread3 drvs))))
+
+    ;; This test should complete in less than a minute; if not, there's a
+    ;; deadlock.
+    (let ((deadline (+ (current-time) 120)))
+      (list (join-thread thread1 deadline 'timeout)
+            (join-thread thread2 deadline 'timeout)
+            (join-thread thread3 deadline 'timeout)))))
+
+(test-end)