Index: head/lib/libc/tests/gen/Makefile
===================================================================
--- head/lib/libc/tests/gen/Makefile
+++ head/lib/libc/tests/gen/Makefile
@@ -35,11 +35,12 @@
 
 CFLAGS+=	-DTEST_LONG_DOUBLE
 
-# Not sure why this isn't defined for all architectures, since most
-# have long double.
+# Define __HAVE_LONG_DOUBLE for architectures whose long double has greater
+# precision than their double.
 .if ${MACHINE_CPUARCH} == "aarch64" || \
     ${MACHINE_CPUARCH} == "amd64" || \
-    ${MACHINE_CPUARCH} == "i386"
+    ${MACHINE_CPUARCH} == "i386" || \
+    ${MACHINE_CPUARCH} == "riscv"
 CFLAGS+=	-D__HAVE_LONG_DOUBLE
 .endif
 
Index: head/lib/libc/tests/stdlib/Makefile
===================================================================
--- head/lib/libc/tests/stdlib/Makefile
+++ head/lib/libc/tests/stdlib/Makefile
@@ -19,11 +19,12 @@
 # All architectures on FreeBSD have fenv.h
 CFLAGS+=	-D__HAVE_FENV
 
-# Not sure why this isn't defined for all architectures, since most
-# have long double.
+# Define __HAVE_LONG_DOUBLE for architectures whose long double has greater
+# precision than their double.
 .if ${MACHINE_CPUARCH} == "aarch64" || \
     ${MACHINE_CPUARCH} == "amd64" || \
-    ${MACHINE_CPUARCH} == "i386"
+    ${MACHINE_CPUARCH} == "i386" || \
+    ${MACHINE_CPUARCH} == "riscv"
 CFLAGS+=	-D__HAVE_LONG_DOUBLE
 .endif
 
Index: head/lib/msun/tests/Makefile
===================================================================
--- head/lib/msun/tests/Makefile
+++ head/lib/msun/tests/Makefile
@@ -10,11 +10,12 @@
 # For isqemu.h
 CFLAGS+=	-I${TESTSRC:H}/libc/gen
 
-# Not sure why this isn't defined for all architectures, since most
-# have long double.
+# Define __HAVE_LONG_DOUBLE for architectures whose long double has greater
+# precision than their double.
 .if ${MACHINE_CPUARCH} == "aarch64" || \
     ${MACHINE_CPUARCH} == "amd64" || \
-    ${MACHINE_CPUARCH} == "i386"
+    ${MACHINE_CPUARCH} == "i386" || \
+    ${MACHINE_CPUARCH} == "riscv"
 CFLAGS+=	-D__HAVE_LONG_DOUBLE
 .endif