diff --git a/srcpkgs/thunderbird/patches/ff85-ppc64-xptcall.patch b/srcpkgs/thunderbird/patches/ff85-ppc64-xptcall.patch
new file mode 100644
index 0000000000..b270d836f2
--- /dev/null
+++ b/srcpkgs/thunderbird/patches/ff85-ppc64-xptcall.patch
@@ -0,0 +1,63 @@
+diff --git a/xpcom/reflect/xptcall/md/unix/xptcinvoke_ppc64_linux.cpp b/xpcom/reflect/xptcall/md/unix/xptcinvoke_ppc64_linux.cpp
+--- xpcom/reflect/xptcall/md/unix/xptcinvoke_ppc64_linux.cpp
++++ xpcom/reflect/xptcall/md/unix/xptcinvoke_ppc64_linux.cpp
+@@ -91,7 +91,13 @@
+         if (!s->IsIndirect() && s->type == nsXPTType::T_DOUBLE) {
+             if (nr_fpr < FPR_COUNT) {
+                 fpregs[nr_fpr++] = s->val.d;
+-                nr_gpr++;
++                // Even if we have enough FPRs, still skip space in
++                // the parameter area if we ran out of placeholder GPRs.
++                if (nr_gpr < GPR_COUNT) {
++                    nr_gpr++;
++                } else {
++                    d++;
++                }
+             } else {
+                 *((double *)d) = s->val.d;
+                 d++;
+@@ -101,7 +107,11 @@
+             if (nr_fpr < FPR_COUNT) {
+                 // Single-precision floats are passed in FPRs too.
+                 fpregs[nr_fpr++] = s->val.f;
+-                nr_gpr++;
++                if (nr_gpr < GPR_COUNT) {
++                    nr_gpr++;
++                } else {
++                    d++;
++                }
+             } else {
+ #ifdef __LITTLE_ENDIAN__
+                 *((float *)d) = s->val.f;
+diff --git a/xpcom/reflect/xptcall/md/unix/xptcstubs_ppc64_linux.cpp b/xpcom/reflect/xptcall/md/unix/xptcstubs_ppc64_linux.cpp
+--- xpcom/reflect/xptcall/md/unix/xptcstubs_ppc64_linux.cpp
++++ xpcom/reflect/xptcall/md/unix/xptcstubs_ppc64_linux.cpp
+@@ -103,7 +103,13 @@
+         if (!param.IsOut() && type == nsXPTType::T_DOUBLE) {
+             if (nr_fpr < FPR_COUNT) {
+                 dp->val.d = fpregs[nr_fpr++];
+-                nr_gpr++;
++                // Even if we have enough FPRs, still skip space in
++                // the parameter area if we ran out of placeholder GPRs.
++                if (nr_gpr < GPR_COUNT) {
++                    nr_gpr++;
++                } else {
++                    ap++;
++                }
+             } else {
+                 dp->val.d = *(double*)ap++;
+             }
+@@ -113,7 +119,11 @@
+             if (nr_fpr < FPR_COUNT) {
+                 // Single-precision floats are passed in FPRs too.
+                 dp->val.f = (float)fpregs[nr_fpr++];
+-                nr_gpr++;
++                if (nr_gpr < GPR_COUNT) {
++                    nr_gpr++;
++                } else {
++                    ap++;
++                }
+             } else {
+ #ifdef __LITTLE_ENDIAN__
+                 dp->val.f = *(float*)ap++;
+