diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -925,6 +925,12 @@
       }
       uint64_t add = r.addend;
       if (auto *sym = cast_or_null<Defined>(r.referent.dyn_cast<Symbol *>())) {
+        // Check whether the symbol defined in this file is the prevailing one.
+        // Skip if it is e.g. a weak def that didn't prevail.
+        if (sym->getFile() != this) {
+          ++it;
+          continue;
+        }
         add += sym->value;
         referentIsec = cast<ConcatInputSection>(sym->isec);
       } else {
diff --git a/lld/test/MachO/weak-definition-gc.s b/lld/test/MachO/weak-definition-gc.s
--- a/lld/test/MachO/weak-definition-gc.s
+++ b/lld/test/MachO/weak-definition-gc.s
@@ -30,19 +30,29 @@
 ## Test that omitted weak symbols don't add entries to the compact unwind table.
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin19.0.0 %t/weak-sub-lsda.s -o %t/weak-sub-lsda.o
 # RUN: %lld -dylib -lc++ -o %t/out.dylib %t/weak-sub-lsda.o %t/weak-sub-lsda.o
-# RUN: llvm-objdump --macho --unwind-info --syms %t/out.dylib | FileCheck %s --check-prefix=UNWIND -D#%x,BASE=0
-
-# UNWIND:      SYMBOL TABLE:
-# UNWIND-DAG:  [[#%x,FOO:]]       w  F __TEXT,__text _foo
-# UNWIND-NOT:                          __TEXT,__text _foo
-
-# UNWIND:      Contents of __unwind_info section:
-# UNWIND:        LSDA descriptors:
-# UNWIND:           [0]: function offset=0x[[#%.8x,FOO-BASE]]
-# UNWIND-NOT:       [1]:
-# UNWIND:        Second level indices:
-# UNWIND-DAG:      [0]: function offset=0x[[#%.8x,FOO-BASE]]
-# UNWIND-NOT:      [1]:
+# RUN: llvm-objdump --macho --unwind-info --syms %t/out.dylib | FileCheck %s --check-prefix=ONE-UNWIND
+# RUN: %lld -dylib -lc++ -o %t/out.dylib %t/weak-sub.o %t/weak-sub-lsda.o
+# RUN: llvm-objdump --macho --unwind-info --syms %t/out.dylib | FileCheck %s --check-prefix=NO-UNWIND
+# RUN: yaml2obj %t/weak-sub-lsda-r.yaml -o %t/weak-sub-lsda-r.o
+# RUN: %lld -dylib -lc++ -o %t/out.dylib %t/weak-sub.o %t/weak-sub-lsda-r.o
+# RUN: llvm-objdump --macho --unwind-info --syms %t/out.dylib | FileCheck %s --check-prefix=NO-UNWIND
+
+# ONE-UNWIND:      SYMBOL TABLE:
+# ONE-UNWIND-DAG:  [[#%x,FOO:]]       w  F __TEXT,__text _foo
+# ONE-UNWIND-NOT:                          __TEXT,__text _foo
+
+# ONE-UNWIND:      Contents of __unwind_info section:
+# ONE-UNWIND:        LSDA descriptors:
+# ONE-UNWIND:           [0]: function offset=0x[[#%.8x,FOO]]
+# ONE-UNWIND-NOT:       [1]:
+# ONE-UNWIND:        Second level indices:
+# ONE-UNWIND-DAG:      [0]: function offset=0x[[#%.8x,FOO]]
+# ONE-UNWIND-NOT:      [1]:
+
+# NO-UNWIND:      SYMBOL TABLE:
+# NO-UNWIND-DAG:  [[#%x,FOO:]]       w  F __TEXT,__text _foo
+# NO-UNWIND-NOT:                          __TEXT,__text _foo
+# NO-UNWIND-NOT:  Contents of __unwind_info section:
 
 ## Test interaction with .alt_entry
 ## FIXME: ld64 manages to strip both one copy of _foo and _bar each.
@@ -246,3 +256,220 @@
   retq
 
 .subsections_via_symbols
+
+#--- weak-sub-lsda-r.yaml
+## This was generated from compiling weak-sub-lsda.s above at rev a2404f11c77e
+## and then running it through `ld -r`. This converts a number of unwind-related
+## relocations from section- to symbol-based ones.
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x1000007
+  cpusubtype:      0x3
+  filetype:        0x1
+  ncmds:           2
+  sizeofcmds:      464
+  flags:           0x2000
+  reserved:        0x0
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         392
+    segname:         ''
+    vmaddr:          0
+    vmsize:          152
+    fileoff:         528
+    filesize:        152
+    maxprot:         7
+    initprot:        7
+    nsects:          3
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x0
+        size:            6
+        offset:          0x210
+        align:           0
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         554889E55DC3
+      - sectname:        __gcc_except_tab
+        segname:         __TEXT
+        addr:            0x6
+        size:            32
+        offset:          0x216
+        align:           0
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x0
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         '0000000000000000000000000000000000000000000000000000000000000000'
+      - sectname:        __eh_frame
+        segname:         __TEXT
+        addr:            0x28
+        size:            80
+        offset:          0x238
+        align:           3
+        reloff:          0x2A8
+        nreloc:          7
+        flags:           0x0
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         1C00000000000000017A504C5200017810079B0400000010100C0708900100002C00000004000000F8FFFFFFFFFFFFFF060000000000000008E7FFFFFFFFFFFFFF410E800111067A430D060000000000
+        relocations:
+          - address:         0x13
+            symbolnum:       5
+            pcrel:           true
+            length:          2
+            extern:          true
+            type:            4
+            scattered:       false
+            value:           0
+          - address:         0x24
+            symbolnum:       2
+            pcrel:           false
+            length:          2
+            extern:          true
+            type:            5
+            scattered:       false
+            value:           0
+          - address:         0x24
+            symbolnum:       3
+            pcrel:           false
+            length:          2
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+          - address:         0x28
+            symbolnum:       3
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            5
+            scattered:       false
+            value:           0
+          - address:         0x28
+            symbolnum:       4
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+          - address:         0x39
+            symbolnum:       3
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            5
+            scattered:       false
+            value:           0
+          - address:         0x39
+            symbolnum:       1
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+      - sectname:        __compact_unwind
+        segname:         __LD
+        addr:            0x78
+        size:            32
+        offset:          0x288
+        align:           3
+        reloff:          0x2E0
+        nreloc:          4
+        flags:           0x2000000
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         '0000000000000000060000000000004100000000000000000000000000000000'
+        relocations:
+          - address:         0x0
+            symbolnum:       4
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+          - address:         0x18
+            symbolnum:       1
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+          - address:         0x10
+            symbolnum:       5
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+          - address:         0x18
+            symbolnum:       1
+            pcrel:           false
+            length:          3
+            extern:          true
+            type:            0
+            scattered:       false
+            value:           0
+  - cmd:             LC_SYMTAB
+    cmdsize:         24
+    symoff:          768
+    nsyms:           6
+    stroff:          864
+    strsize:         57
+LinkEditData:
+  NameList:
+    - n_strx:          29
+      n_type:          0xE
+      n_sect:          2
+      n_desc:          0
+      n_value:         6
+    - n_strx:          34
+      n_type:          0xE
+      n_sect:          2
+      n_desc:          0
+      n_value:         22
+    - n_strx:          39
+      n_type:          0xE
+      n_sect:          3
+      n_desc:          0
+      n_value:         40
+    - n_strx:          49
+      n_type:          0xE
+      n_sect:          3
+      n_desc:          0
+      n_value:         72
+    - n_strx:          2
+      n_type:          0xF
+      n_sect:          1
+      n_desc:          128
+      n_value:         0
+    - n_strx:          7
+      n_type:          0x1
+      n_sect:          0
+      n_desc:          0
+      n_value:         0
+  StringTable:
+    - ' '
+    - _foo
+    - ___gxx_personality_v0
+    - l001
+    - l002
+    - EH_Frame1
+    - func.eh
+...