diff --git a/lld/ELF/Compartments.cpp b/lld/ELF/Compartments.cpp
index c9e6874699e08..7d87133dbe92e 100644
--- a/lld/ELF/Compartments.cpp
+++ b/lld/ELF/Compartments.cpp
@@ -479,21 +479,60 @@ void assignSectionsToCompartments() {
     assert(s->file->compartment == 0);
 
     StringRef path = s->file->getName();
-    Expected<Compartment &> c = fileLookup.findMatch(path);
-    if (!c) {
-      error("input file " + path + " " + toString(c.takeError()));
-      valid = false;
-      continue;
+    StringRef scope = s->file->archiveName;
+    StringRef scopedPath = path;
+    std::string scopedStr;
+    if (!scope.empty()) {
+      scopedStr = (scope + ":" + path).str();
+      scopedPath = scopedStr;
     }
-
-    // If the path is not a basename, try to match on the basename.
-    if (c->isDefault() && llvm::sys::path::has_parent_path(path)) {
-      c = fileLookup.findMatch(llvm::sys::path::filename(path));
+    Expected<Compartment &> c = *defaultCompart;
+    handleAllErrors(c.takeError());
+    auto tryMatch = [&](StringRef s) -> bool {
+      llvm::errs() << "tryMatch: " << s << "\n";
+      c = fileLookup.findMatch(s);
       if (!c) {
-        error("input file " + path + " " + toString(c.takeError()));
+        error("input file " + scopedPath + " " + toString(c.takeError()));
         valid = false;
+        return false;
+      }
+      return true;
+    };
+
+    // When matching, give precedence to full-path matches for the archive
+    // name (for archive members) or file name (for standalone input files).
+
+    // For archive members, require the pattern to include the name of the
+    // archive with an optional colon-prefixed suffix of the member name.
+    if (!scope.empty()) {
+      // First, try to match a fully scoped <archive>:<member>.
+      if (!tryMatch(scopedPath))
+        continue;
+
+      // Second, match on just the archive name.
+      if (c->isDefault() && !tryMatch(scope))
         continue;
+
+      // If the archive path is not a basename, try to match with a scope of
+      // just the basename.
+      if (c->isDefault() && llvm::sys::path::has_parent_path(scope)) {
+        StringRef baseScope = llvm::sys::path::filename(scope);
+        if (!tryMatch((baseScope + ":" + path).str()))
+          continue;
+
+        // Try to match just the archive basename.
+        if (c->isDefault() && !tryMatch(baseScope))
+          continue;
       }
+    } else {
+      // Prioritise matches with a full path.
+      if (c->isDefault() && !tryMatch(path))
+        continue;
+
+      // If the path is not a basename, try to match on the basename.
+      if (c->isDefault() && llvm::sys::path::has_parent_path(path) &&
+          !tryMatch(llvm::sys::path::filename(path)))
+        continue;
     }
 
     if (c->isDefault())
@@ -501,7 +540,7 @@ void assignSectionsToCompartments() {
 
     s->file->compartment = c->getNumber();
     if (config->verboseCompartmentalization)
-      message("info: input file " + s->file->getName() + " matched to " +
+      message("info: input file " + scopedPath + " matched to " +
               compartmentName(*c));
   }
 
diff --git a/lld/test/ELF/cheri/riscv/c18n/static-lib.s b/lld/test/ELF/cheri/riscv/c18n/static-lib.s
new file mode 100644
index 0000000000000..7dd5ca4258db5
--- /dev/null
+++ b/lld/test/ELF/cheri/riscv/c18n/static-lib.s
@@ -0,0 +1,79 @@
+# REQUIRES: riscv
+
+# RUN: rm -rf %t && split-file %s %t
+
+# RUN: %riscv64_cheri_purecap_llvm-mc -filetype=obj %t/a.s -o %t/a.o
+# RUN: %riscv64_cheri_purecap_llvm-mc -filetype=obj %t/b.s -o %t/b.o
+# RUN: llvm-ar crs %t/libb.a %t/b.o
+# RUN: ld.lld -o %t/fully-scoped %t/a.o %t/libb.a \
+# RUN:   --compartment-policy=%t/fully-scoped.json
+# RUN: ld.lld -o %t/scope-only %t/a.o %t/libb.a \
+# RUN:   --compartment-policy=%t/scope-only.json
+# RUN: not ld.lld -o %t/unscoped %t/a.o %t/libb.a \
+# RUN:   --compartment-policy=%t/unscoped.json 2>&1 | \
+# RUN:	 FileCheck %s --check-prefix=UNSCOPED
+# RUN: llvm-readelf -l %t/fully-scoped | FileCheck %s --check-prefix=SCOPED
+# RUN: llvm-readelf -l %t/scope-only | FileCheck %s --check-prefix=SCOPED
+
+# SCOPED-LABEL: Program Headers:
+# SCOPED-NEXT:    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
+# SCOPED-NEXT:    PHDR           0x000040 0x0000000000010040 0x0000000000010040 0x000150 0x000150 R   0x8
+# SCOPED-NEXT:    LOAD           0x000000 0x0000000000010000 0x0000000000010000 0x000195 0x000195 R   0x1000
+# SCOPED-NEXT:    LOAD           0x000198 0x0000000000011198 0x0000000000011198 0x00000c 0x00000c R E 0x1000
+# SCOPED-NEXT:    C18N_NAME      0x000198 0x0000000000011198 0x0000000000000001 0x00000c 0x00000c     0x4
+# SCOPED-NEXT:        [Compartment: one]
+# SCOPED-NEXT:    CHERI_PCC      0x000198 0x0000000000011198 0x0000000000011198 0x00000c 0x00000c R E 0x4
+# SCOPED-NEXT:    GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x0
+
+# SCOPED-LABEL:  Section to Segment mapping:
+# SCOPED-NEXT:    Segment Sections...
+# SCOPED-NEXT:     00
+# SCOPED-NEXT:     01     .c18nstrtab
+# SCOPED-NEXT:     02     .text.one
+# SCOPED-NEXT:     03     .text.one
+# SCOPED-NEXT:     04     .text.one
+# SCOPED-NEXT:     05
+# SCOPED-NEXT:     None   .pad.cheri.pcc.one .comment .symtab .shstrtab .strtab
+
+# UNSCOPED: error: no output sections for compartment one
+
+#--- a.s
+
+call foo
+
+#--- b.s
+
+.global foo
+.type foo, %function
+foo:
+  ret
+
+#--- fully-scoped.json
+
+{
+  "compartments": {
+    "one": {
+      "files": ["libb.a:b.o"]
+    }
+  }
+}
+
+#--- scope-only.json
+
+{
+  "compartments": {
+    "one": {
+      "files": ["libb.a"]
+    }
+  }
+}
+
+#--- unscoped.json
+
+{
+  "compartments": {
+    "one": {
+      "files": ["b.o"]
+    }
+  }
+}