Index: lld/MachO/InputFiles.cpp
===================================================================
--- lld/MachO/InputFiles.cpp
+++ lld/MachO/InputFiles.cpp
@@ -580,6 +580,7 @@
       return nList[lhs].n_value < nList[rhs].n_value;
     });
     uint64_t sectionAddr = sectionHeaders[i].addr;
+    uint32_t sectionAlign = 1u << sectionHeaders[i].align;
 
     // We populate subsecMap by repeatedly splitting the last (highest address)
     // subsection.
@@ -622,7 +623,7 @@
       // TODO: ld64 appears to preserve the original alignment as well as each
       // subsection's offset from the last aligned address. We should consider
       // emulating that behavior.
-      nextIsec->align = MinAlign(isec->align, sym.n_value);
+      nextIsec->align = MinAlign(sectionAlign, sym.n_value);
       subsecMap.push_back({sym.n_value - sectionAddr, nextIsec});
       subsecEntry = subsecMap.back();
     }
Index: lld/test/MachO/weak-definition-gc.s
===================================================================
--- lld/test/MachO/weak-definition-gc.s
+++ lld/test/MachO/weak-definition-gc.s
@@ -53,6 +53,19 @@
 # RUN: %lld -dylib -o %t/out.dylib %t/weak-sub-alt.o %t/weak-sub-alt2.o
 # RUN: %lld -dylib -o %t/out.dylib %t/weak-sub-alt2.o %t/weak-sub-alt.o
 
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin19.0.0 %t/weak-aligned-1.s -o %t/weak-aligned-1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin19.0.0 %t/weak-aligned-2.s -o %t/weak-aligned-2.o
+# RUN: %lld -o %t/out -lSystem %t/weak-aligned-1.o %t/weak-aligned-2.o
+# RUN: llvm-objdump --syms --section=__const --full-contents %t/out | FileCheck --check-prefix=ALIGN %s
+# ALIGN:      SYMBOL TABLE:
+# ALIGN-DAG:  [[#%x, ADDR:]]       l     O __DATA_CONST,__const _weak1
+# ALIGN-DAG:  {{0*}}[[#ADDR+ 0x4]] l     O __DATA_CONST,__const _weak3
+# ALIGN-DAG:  {{0*}}[[#ADDR+ 0x8]] l     O __DATA_CONST,__const _weak2
+# ALIGN-DAG:  {{0*}}[[#ADDR+0x10]] g     O __DATA_CONST,__const _aligned
+# ALIGN:      Contents of section __DATA_CONST,__const:
+# ALIGN-NEXT: {{0*}}[[#ADDR]]      11111111 33333333 22222222 00000000  ....3333""""....
+# ALIGN-NEXT: {{0*}}[[#ADDR+0x10]] 81818181 81818181 82828282 82828282  ................
+
 #--- weak-sub.s
 .globl _foo, _bar
 .weak_definition _foo, _bar
@@ -129,3 +142,56 @@
   callq _bar
 
 .subsections_via_symbols
+
+#--- weak-aligned-1.s
+.section __DATA,__const
+.p2align 3
+.globl _weak1
+.weak_def_can_be_hidden _weak1
+_weak1:
+  .4byte 0x11111111
+
+.globl _weak3
+.weak_def_can_be_hidden _weak3
+_weak3:
+  .4byte 0x33333333
+
+.subsections_via_symbols
+
+#--- weak-aligned-2.s
+# _weak1 and _weak3 are already in weak-aligned-1,
+# so from _weak1-3 in this file only _weak2 is used.
+# However, _aligned still has to stay aligned to a 16-byte boundary.
+.section __DATA,__const
+.p2align 3
+.globl _weak1
+.weak_def_can_be_hidden _weak1
+_weak1:
+  .4byte 0x11111111
+
+.globl _weak2
+.weak_def_can_be_hidden _weak2
+_weak2:
+  .4byte 0x22222222
+
+.globl _weak3
+.weak_def_can_be_hidden _weak3
+_weak3:
+  .4byte 0x33333333
+
+.section __DATA,__const
+.p2align 4
+.globl _aligned
+_aligned:
+  .8byte 0x8181818181818181
+  .8byte 0x8282828282828282
+
+.section __TEXT,__text
+.globl _main
+_main:
+  movl _weak1(%rip), %eax
+  movl _weak2(%rip), %ebx
+  movaps _aligned(%rip), %xmm0
+  retq
+
+.subsections_via_symbols