diff --git a/src/build/build_step.go b/src/build/build_step.go
index b2c8e4c05..1468dc1c8 100644
--- a/src/build/build_step.go
+++ b/src/build/build_step.go
@@ -185,6 +185,17 @@ func buildTarget(state *core.BuildState, target *core.BuildTarget, runRemotely b
 			return err
 		}
 		log.Debug("Finished pre-build function for %s", target.Label)
+
+		// Wait for any new dependencies added by pre-build commands before continuing.
+		for _, dep := range target.Dependencies() {
+			dep.WaitForBuild(target.Label)
+			if dep.State() >= core.DependencyFailed { // Either the target failed or its dependencies failed
+				// Give up and set the original target as dependency failed
+				target.SetState(core.DependencyFailed)
+				return fmt.Errorf("error in pre-rule dependency for %s: %s", target.Label, dep.Label)
+			}
+		}
+		log.Debug("Finished waiting for dependencies for %s", target.Label)
 	}
 
 	state.LogBuildResult(target, core.TargetBuilding, "Preparing...")
@@ -343,6 +354,16 @@ func buildTarget(state *core.BuildState, target *core.BuildTarget, runRemotely b
 			return err
 		}
 
+		// Wait for any new dependencies added by post-build commands before continuing.
+		for _, dep := range target.Dependencies() {
+			dep.WaitForBuild(target.Label)
+			if dep.State() >= core.DependencyFailed { // Either the target failed or its dependencies failed
+				// Give up and set the original target as dependency failed
+				target.SetState(core.DependencyFailed)
+				return fmt.Errorf("error in post-rule dependency for %s: %s", target.Label, dep.Label)
+			}
+		}
+
 		if runRemotely && len(outs) != len(target.Outputs()) {
 			// postBuildFunction has changed the target - must rebuild it
 			log.Info("Rebuilding %s after post-build function", target)
diff --git a/src/core/build_input.go b/src/core/build_input.go
index 010e047b0..d066338fc 100644
--- a/src/core/build_input.go
+++ b/src/core/build_input.go
@@ -220,6 +220,51 @@ func (label SystemPathLabel) String() string {
 	return label.Name
 }
 
+// SingleOutputLabel represents a build label for a specific output of a rule.
+// This can be used to target a specific output of this rule when depended on or an entry point when used in
+// the context of tools.
+type SingleOutputLabel struct {
+	BuildLabel
+	Output string
+}
+
+// MarshalText implements the encoding.TextMarshaler interface, which makes AnnotatedOutputLabel
+// usable as map keys in JSON.
+func (label SingleOutputLabel) MarshalText() ([]byte, error) {
+	return []byte(label.String()), nil
+}
+
+// Paths returns a slice of paths to the files of this input.
+func (label SingleOutputLabel) Paths(graph *BuildGraph) []string {
+	target := graph.TargetOrDie(label.BuildLabel)
+	return addPathPrefix([]string{label.Output}, target.PackageDir())
+}
+
+// FullPaths is like Paths but includes the leading plz-out/gen directory.
+func (label SingleOutputLabel) FullPaths(graph *BuildGraph) []string {
+	target := graph.TargetOrDie(label.BuildLabel)
+	return addPathPrefix([]string{label.Output}, target.OutDir())
+}
+
+// LocalPaths returns paths within the local package
+func (label SingleOutputLabel) LocalPaths(graph *BuildGraph) []string {
+	return []string{label.Output}
+}
+
+// Label returns the build rule associated with this input. For a SingleOutputLabel it's always non-nil.
+func (label SingleOutputLabel) Label() (BuildLabel, bool) {
+	return label.BuildLabel, true
+}
+
+func (label SingleOutputLabel) nonOutputLabel() (BuildLabel, bool) {
+	return BuildLabel{}, false
+}
+
+// String returns a string representation of this input.
+func (label SingleOutputLabel) String() string {
+	return label.BuildLabel.String() + "+" + label.Output
+}
+
 // AnnotatedOutputLabel represents a build label with an annotation e.g. //foo:bar|baz where baz constitutes the
 // annotation. This can be used to target a named output of this rule when depended on or an entry point when used in
 // the context of tools.
diff --git a/src/core/build_target.go b/src/core/build_target.go
index 5e523be46..8fc7284f2 100644
--- a/src/core/build_target.go
+++ b/src/core/build_target.go
@@ -1664,6 +1664,16 @@ func (target *BuildTarget) AddMaybeExportedDependency(dep BuildLabel, exported,
 	}
 }
 
+// RegisterDependencyTarget registers a build target to be used for a dependency label on the given target.
+func (target *BuildTarget) RegisterDependencyTarget(dep BuildLabel, deptarget *BuildTarget) {
+	info := target.dependencyInfo(dep)
+	if info == nil {
+		log.Fatalf("Target %s doesn't contain dependency %s.\n", target.Label, dep)
+	} else {
+		info.deps = append(info.deps, deptarget)
+	}
+}
+
 // IsTool returns true if the given build label is a tool used by this target.
 func (target *BuildTarget) IsTool(tool BuildLabel) bool {
 	if target.isTool(tool, target.Tools, target.namedTools) {
diff --git a/src/parse/asp/builtins.go b/src/parse/asp/builtins.go
index 7562efd60..4231ab8fa 100644
--- a/src/parse/asp/builtins.go
+++ b/src/parse/asp/builtins.go
@@ -1151,6 +1151,7 @@ func addDep(s *scope, args []pyObject) pyObject {
 	dep := s.parseLabelInPackage(string(args[1].(pyString)), s.pkg)
 	exported := args[2].IsTruthy()
 	target.AddMaybeExportedDependency(dep, exported, false, false)
+	target.RegisterDependencyTarget(dep, s.state.Graph.Target(dep))
 	// Queue this dependency if it'll be needed.
 	if target.State() > core.Inactive {
 		err := s.state.QueueTarget(dep, target.Label, false, core.ParseModeNormal)
diff --git a/src/parse/asp/interpreter.go b/src/parse/asp/interpreter.go
index 218815615..c09cb4ac4 100644
--- a/src/parse/asp/interpreter.go
+++ b/src/parse/asp/interpreter.go
@@ -310,6 +310,16 @@ type scope struct {
 // parseAnnotatedLabelInPackage similarly to parseLabelInPackage, parses the label contextualising it to the provided
 // package. It may return an AnnotatedOutputLabel or a BuildLabel depending on if the label is annotated.
 func (s *scope) parseAnnotatedLabelInPackage(label string, pkg *core.Package) core.BuildInput {
+	if strings.Contains(label, "+") {
+		parts := strings.Split(label, "+")
+		if len(parts) == 2 {
+			return core.SingleOutputLabel{
+				BuildLabel: s.parseLabelInPackage(parts[0], pkg),
+				Output:     parts[1],
+			}
+		}
+	}
+
 	label, annotation := core.SplitLabelAnnotation(label)
 	if annotation != "" {
 		return core.AnnotatedOutputLabel{