diff --git a/programs/GNUmakefile b/programs/GNUmakefile
index 82a2b59..42dcb26 100644
--- a/programs/GNUmakefile
+++ b/programs/GNUmakefile
@@ -216,8 +216,8 @@ login: bearssl libc
 shell:
 	$(MAKE) -C src/shell
 
-# Build desktop via its own Makefile (depends on libc, libjpeg, and bearssl for user.h).
-desktop: libc libjpeg bearssl
+# Build desktop via its own Makefile (depends on libc, libjpeg, bearssl for user.h, and dialogs for duplicate-session warnings).
+desktop: libc libjpeg bearssl libloader dialogs
 	$(MAKE) -C src/desktop
 
 # Copy SVG icons for the desktop into bin/icons/.
diff --git a/programs/src/desktop/Makefile b/programs/src/desktop/Makefile
index 681de9a..6446377 100644
--- a/programs/src/desktop/Makefile
+++ b/programs/src/desktop/Makefile
@@ -19,6 +19,7 @@ PROG_INC := ../../include
 JPEG_LIB := ../../lib/libjpeg
 LIBC_LIB := ../../lib/libc
 BEARSSL  := ../../lib/bearssl
+LOADER_LIB := ../../bin/liblibloader.a
 LINK_LD  := ../../link.ld
 BINDIR   := ../../bin
 OBJDIR   := obj
@@ -82,7 +83,7 @@ all: $(TARGET)
 
 # ---- Libraries ----
 
-LIBS := $(JPEG_LIB)/libjpeg.a $(BEARSSL)/libbearssl.a $(LIBC_LIB)/liblibc.a
+LIBS := $(LOADER_LIB) $(JPEG_LIB)/libjpeg.a $(BEARSSL)/libbearssl.a $(LIBC_LIB)/liblibc.a
 
 $(TARGET): $(OBJS) $(LIBS) $(LINK_LD) Makefile
 	mkdir -p $(BINDIR)/os
diff --git a/programs/src/desktop/main.cpp b/programs/src/desktop/main.cpp
index ae555a3..dace1bb 100644
--- a/programs/src/desktop/main.cpp
+++ b/programs/src/desktop/main.cpp
@@ -8,6 +8,7 @@
 #include <montauk/config.h>
 #include <montauk/user.h>
 #include <gui/clipboard.hpp>
+#include <gui/dialogs.hpp>
 
 // ============================================================================
 // App Manifest Scanning
@@ -642,7 +643,46 @@ void gui::desktop_run(DesktopState* ds) {
 
 static DesktopState* g_desktop;
 
+static constexpr const char kDesktopBinaryName[] = "desktop.elf";
+static constexpr int DESKTOP_PROC_SCAN_MAX = 256;
+
+static bool desktop_proc_alive(const Montauk::ProcInfo& proc) {
+    return proc.state == 1 || proc.state == 2 || proc.state == 3;
+}
+
+static bool proc_name_is_desktop(const char* name) {
+    int name_len = montauk::slen(name);
+    int binary_len = (int)sizeof(kDesktopBinaryName) - 1;
+    if (name_len < binary_len) return false;
+
+    const char* suffix = name + name_len - binary_len;
+    if (!montauk::streq(suffix, kDesktopBinaryName)) return false;
+    return name_len == binary_len || suffix[-1] == '/';
+}
+
+static bool existing_desktop_running() {
+    static Montauk::ProcInfo procs[DESKTOP_PROC_SCAN_MAX];
+    int count = montauk::proclist(procs, DESKTOP_PROC_SCAN_MAX);
+    if (count <= 0) return false;
+
+    int self_pid = montauk::getpid();
+    for (int i = 0; i < count; i++) {
+        if (procs[i].pid == self_pid) continue;
+        if (!desktop_proc_alive(procs[i])) continue;
+        if (proc_name_is_desktop(procs[i].name)) return true;
+    }
+    return false;
+}
+
 extern "C" void _start() {
+    if (existing_desktop_running()) {
+        gui::dialogs::message_box(
+            "Desktop Already Running",
+            "Cannot spawn new desktop process whilst an existing desktop session is active.",
+            gui::dialogs::MESSAGE_BOX_OK);
+        montauk::exit(0);
+    }
+
     DesktopState* ds = (DesktopState*)montauk::malloc(sizeof(DesktopState));
     montauk::memset(ds, 0, sizeof(DesktopState));