Index: lld/COFF/Writer.cpp
===================================================================
--- lld/COFF/Writer.cpp
+++ lld/COFF/Writer.cpp
@@ -1864,6 +1864,10 @@
   uint8_t *end = bufAddr(lastPdata) + lastPdata->getSize();
   if (config->machine == AMD64) {
     struct Entry { ulittle32_t begin, end, unwind; };
+    if ((end - begin) % sizeof(Entry) != 0) {
+      fatal("unexpected .pdata size: " + std::to_string(end - begin) +
+            " is not a multiple of " + std::to_string(sizeof(Entry)));
+    }
     parallelSort(
         MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
         [](const Entry &a, const Entry &b) { return a.begin < b.begin; });
@@ -1871,6 +1875,10 @@
   }
   if (config->machine == ARMNT || config->machine == ARM64) {
     struct Entry { ulittle32_t begin, unwind; };
+    if ((end - begin) % sizeof(Entry) != 0) {
+      fatal("unexpected .pdata size: " + std::to_string(end - begin) +
+            " is not a multiple of " + std::to_string(sizeof(Entry)));
+    }
     parallelSort(
         MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
         [](const Entry &a, const Entry &b) { return a.begin < b.begin; });
Index: lld/test/COFF/pdata-arm64-bad.yaml
===================================================================
--- /dev/null
+++ lld/test/COFF/pdata-arm64-bad.yaml
@@ -0,0 +1,90 @@
+# RUN: yaml2obj < %s > %t.obj
+#
+# RUN: not lld-link /out:%t.exe /entry:func1 /subsystem:console %t.obj 2>&1 | FileCheck %s
+
+# This file is like pdata-arm64.yaml, except that .pdata has been extended with
+# 4 bytes. This can happen due to for example bad assembler input. Check that
+# lld errors gracefully instead of crashing.
+
+# CHECK: unexpected .pdata size: 20 is not a multiple of 8
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_ARM64
+  Characteristics: [  ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     ff4300d1f37b00a9f303012a00000094e003132a00000094f37b40a9ff430091c0035fd6f353bea9fe0b00f9f303012af403022a00000094e003132a00000094e003142a00000094fe0b40f9f353c2a8c0035fd6c0035fd6
+    Relocations:
+      - VirtualAddress:  12
+        SymbolName:      func3
+        Type:            IMAGE_REL_ARM64_BRANCH26
+      - VirtualAddress:  20
+        SymbolName:      func3
+        Type:            IMAGE_REL_ARM64_BRANCH26
+      - VirtualAddress:  52
+        SymbolName:      func3
+        Type:            IMAGE_REL_ARM64_BRANCH26
+      - VirtualAddress:  60
+        SymbolName:      func3
+        Type:            IMAGE_REL_ARM64_BRANCH26
+      - VirtualAddress:  68
+        SymbolName:      func3
+        Type:            IMAGE_REL_ARM64_BRANCH26
+  - Name:            .pdata
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     0000000031002201000000002500a10000000000
+    Relocations:
+      - VirtualAddress:  0
+        SymbolName:      func2
+        Type:            IMAGE_REL_ARM64_ADDR32NB
+      - VirtualAddress:  8
+        SymbolName:      func1
+        Type:            IMAGE_REL_ARM64_ADDR32NB
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          57
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          1
+  - Name:            .pdata
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          20
+      NumberOfRelocations: 2
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          2
+  - Name:            func1
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            func2
+    Value:           36
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            func3
+    Value:           84
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...