diff --git a/liba/Makefile b/liba/Makefile
index ee0fe2d46..d74dce5ef 100644
--- a/liba/Makefile
+++ b/liba/Makefile
@@ -6,7 +6,9 @@ objs += $(addprefix liba/src/, \
   assert.o \
   errno.o \
   ieee754.o \
+  isnand.o \
   isnanf.o \
+  isinfd.o \
   isinff.o \
   malloc.o \
   memcpy.o \
diff --git a/liba/include/math.h b/liba/include/math.h
index 0f622155b..22aa89bec 100644
--- a/liba/include/math.h
+++ b/liba/include/math.h
@@ -13,13 +13,15 @@ LIBA_BEGIN_DECLS
 /* The C99 standard requires isinf and isnan to be defined as macros that can
  * handle arbitrary precision float numbers. The names of the functions called
  * by those macros (depending on the argument size) are not standardized though.
- * We're chosing isinff/isnanf for single-precision functions (which is the only
- * case we're actually handling). */
+ * We're chosing isinff/isnanf for single-precision functions, and isinfd/isnand
+ * for double-precision functions. */
 
 int isinff(float x);
-#define isinf(x) isinff(x)
+int isinfd(double d);
+#define isinf(x) (sizeof(x) == sizeof(float) ? isinff(x) : isinfd(x))
 int isnanf(float x);
-#define isnan(x) isnanf(x)
+int isnand(double x);
+#define isnan(x) (sizeof(x) == sizeof(float) ? isnanf(x) : isnand(x))
 
 float acosf(float x);
 float acoshf(float x);
diff --git a/liba/include/private/ieee754.h b/liba/include/private/ieee754.h
index e8e567266..4d46d2033 100644
--- a/liba/include/private/ieee754.h
+++ b/liba/include/private/ieee754.h
@@ -3,7 +3,10 @@
 
 #include <stdint.h>
 
-uint32_t ieee754man(float x);
-uint8_t ieee754exp(float x);
+uint32_t ieee754man32(float x);
+uint8_t ieee754exp32(float x);
+
+uint64_t ieee754man64(double x);
+uint16_t ieee754exp64(double x);
 
 #endif
diff --git a/liba/src/ieee754.c b/liba/src/ieee754.c
index a7904f474..19663e662 100644
--- a/liba/src/ieee754.c
+++ b/liba/src/ieee754.c
@@ -1,6 +1,6 @@
 #include <private/ieee754.h>
 
-uint32_t ieee754man(float x) {
+uint32_t ieee754man32(float x) {
   union {
     float f;
     uint32_t i;
@@ -9,7 +9,7 @@ uint32_t ieee754man(float x) {
   return (u.i & ((1<<23)-1));
 }
 
-uint8_t ieee754exp(float x) {
+uint8_t ieee754exp32(float x) {
   union {
     float f;
     uint32_t i;
@@ -17,3 +17,21 @@ uint8_t ieee754exp(float x) {
   u.f = x;
   return (u.i >> 23) & 0xFF;
 }
+
+uint64_t ieee754man64(double x) {
+  union {
+    double d;
+    uint64_t i;
+  } u;
+  u.d = x;
+  return (u.i & (((uint64_t)1<<52)-1));
+}
+
+uint16_t ieee754exp64(double x) {
+  union {
+    double d;
+    uint64_t i;
+  } u;
+  u.d = x;
+  return (uint16_t)((u.i >> 52) & 0x7FF);
+}
diff --git a/liba/src/isinfd.c b/liba/src/isinfd.c
new file mode 100644
index 000000000..67907bbbf
--- /dev/null
+++ b/liba/src/isinfd.c
@@ -0,0 +1,6 @@
+#include <math.h>
+#include <private/ieee754.h>
+
+int isinfd(double x) {
+  return (ieee754exp64(x) == 0x7FF && ieee754man64(x) == 0);
+}
diff --git a/liba/src/isinff.c b/liba/src/isinff.c
index f184f2252..07ffae6cf 100644
--- a/liba/src/isinff.c
+++ b/liba/src/isinff.c
@@ -2,5 +2,5 @@
 #include <private/ieee754.h>
 
 int isinff(float x) {
-  return (ieee754exp(x) == 0xFF && ieee754man(x) == 0);
+  return (ieee754exp32(x) == 0xFF && ieee754man32(x) == 0);
 }
diff --git a/liba/src/isnand.c b/liba/src/isnand.c
new file mode 100644
index 000000000..22e3518e8
--- /dev/null
+++ b/liba/src/isnand.c
@@ -0,0 +1,6 @@
+#include <math.h>
+#include <private/ieee754.h>
+
+int isnand(double x) {
+  return (ieee754exp64(x) == 0x7FF && ieee754man64(x) != 0);
+}
diff --git a/liba/src/isnanf.c b/liba/src/isnanf.c
index 97eb74cec..f524ae486 100644
--- a/liba/src/isnanf.c
+++ b/liba/src/isnanf.c
@@ -2,5 +2,5 @@
 #include <private/ieee754.h>
 
 int isnanf(float x) {
-  return (ieee754exp(x) == 0xFF && ieee754man(x) != 0);
+  return (ieee754exp32(x) == 0xFF && ieee754man32(x) != 0);
 }