Boot Camp assistant hits a SIGSEGV on the second page

I have an old Boot Camp installation (first Windows 7, then upgraded to Windows 10) that I would like to remove. I would like to repartition the Macintosh HD to use the space taken over by said Windows installation. When I open the Boot Camp assistant and click "Continue" on the first assistant page, the assistant crashes with the attached dump. What am I to do?

Process: Boot Camp Assistant [755]

Path: /Applications/Utilities/Boot Camp Assistant.app/Contents/MacOS/Boot Camp Assistant

Identifier: com.apple.bootcampassistant

Version: 6.1.0 (6067.60.1)

Build Info: BootCampAssistant-6067060001000000~5

Code Type: X86-64 (Native)

Parent Process: ??? [1]

Responsible: Boot Camp Assistant [755]

User ID: 501

Date/Time: 2018-09-17 20:03:38.388 +0200

OS Version: Mac OS X 10.13.6 (17G65)

Report Version: 12

Anonymous UUID: 6ABB6106-4975-22B1-3E4F-408927D6A756

Time Awake Since Boot: 1600 seconds

System Integrity Protection: enabled

Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Exception Type: EXC_BAD_ACCESS (SIGSEGV)

Exception Codes: KERN_INVALID_ADDRESS at 0x000054555bf4bec8

Exception Note: EXC_CORPSE_NOTIFY

Termination Signal: Segmentation fault: 11

Termination Reason: Namespace SIGNAL, Code 0xb

Terminating Process: exc handler [0]

VM Regions Near 0x54555bf4bec8:

__LINKEDIT 0000000107adc000-0000000107af7000 [ 108K] r--/rwx SM=COW | [/usr/lib/dyld]

-->

MALLOC_NANO 0000600000000000-0000600000600000 [ 6144K] rw-/rwx SM=PRV

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread

0 libobjc.A.dylib 0x00007fff5265f184 objc_release + 36

1 com.apple.CoreFoundation 0x00007fff2b4ef83e cow_cleanup + 126

2 com.apple.CoreFoundation 0x00007fff2b3ef03d -[__NSArrayM dealloc] + 45

3 libobjc.A.dylib 0x00007fff52660087 (anonymous namespace)::AutoreleasePoolPage::pop(void*) + 817

4 com.apple.CoreFoundation 0x00007fff2b406a06 _CFAutoreleasePoolPop + 22

5 com.apple.Foundation 0x00007fff2d5388ad -[NSAutoreleasePool drain] + 144

6 com.apple.AppKit 0x00007fff289d78e5 -[NSApplication run] + 860

7 com.apple.AppKit 0x00007fff289a6a72 NSApplicationMain + 804

8 libdyld.dylib 0x00007fff53284015 start + 1

Thread 1:

0 libsystem_kernel.dylib 0x00007fff533d528a __workq_kernreturn + 10

1 libsystem_pthread.dylib 0x00007fff5359c20e _pthread_wqthread + 1552

2 libsystem_pthread.dylib 0x00007fff5359bbe9 start_wqthread + 13

Thread 2:

0 libsystem_kernel.dylib 0x00007fff533d528a __workq_kernreturn + 10

1 libsystem_pthread.dylib 0x00007fff5359c20e _pthread_wqthread + 1552

2 libsystem_pthread.dylib 0x00007fff5359bbe9 start_wqthread + 13

Thread 3:

0 libsystem_kernel.dylib 0x00007fff533d528a __workq_kernreturn + 10

1 libsystem_pthread.dylib 0x00007fff5359c20e _pthread_wqthread + 1552

2 libsystem_pthread.dylib 0x00007fff5359bbe9 start_wqthread + 13

Thread 4:

0 libsystem_kernel.dylib 0x00007fff533d528a __workq_kernreturn + 10

1 libsystem_pthread.dylib 0x00007fff5359c20e _pthread_wqthread + 1552

2 libsystem_pthread.dylib 0x00007fff5359bbe9 start_wqthread + 13

Thread 5:

0 libsystem_kernel.dylib 0x00007fff533d528a __workq_kernreturn + 10

1 libsystem_pthread.dylib 0x00007fff5359c009 _pthread_wqthread + 1035

2 libsystem_pthread.dylib 0x00007fff5359bbe9 start_wqthread + 13

Thread 6:

0 libsystem_pthread.dylib 0x00007fff5359bbdc start_wqthread + 0

Thread 7:: com.apple.NSEventThread

0 libsystem_kernel.dylib 0x00007fff533cb20a mach_msg_trap + 10

1 libsystem_kernel.dylib 0x00007fff533ca724 mach_msg + 60

2 com.apple.CoreFoundation 0x00007fff2b448785 __CFRunLoopServiceMachPort + 341

3 com.apple.CoreFoundation 0x00007fff2b447ad7 __CFRunLoopRun + 1783

4 com.apple.CoreFoundation 0x00007fff2b447153 CFRunLoopRunSpecific + 483

5 com.apple.AppKit 0x00007fff28b1ffc4 _NSEventThread + 184

6 libsystem_pthread.dylib 0x00007fff5359c661 _pthread_body + 340

7 libsystem_pthread.dylib 0x00007fff5359c50d _pthread_start + 377

8 libsystem_pthread.dylib 0x00007fff5359bbf9 thread_start + 13

Thread 0 crashed with X86 Thread State (64-bit):

rax: 0x000054555bf4bea8 rbx: 0x00006000000917b0 rcx: 0x0000000000000002 rdx: 0x0000000000000010

rdi: 0x000060000024aaa0 rsi: 0x0000000000000001 rbp: 0x00007ffeef079520 rsp: 0x00007ffeef079520

r8: 0x00007fff8565a8a0 r9: 0x0000000000000000 r10: 0x00007fff8564ff90 r11: 0x00007fdbc30b0c80

r12: 0x0000000000000002 r13: 0x0000604000250da0 r14: 0x00006000000917b0 r15: 0x0000000000000000

rip: 0x00007fff5265f184 rfl: 0x0000000000010202 cr2: 0x000054555bf4bec8

Logical CPU: 2

Error Code: 0x00000004

Trap Number: 14